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9TH MAY, 2005
First of all “why this topic, audio cassettes, only”
Firstly, we have been curious since long that how such a thin magnetic tape
consist of musical notes, how the music is played by the use of magnetic tape
only, how can one magnetic tape be used to play for both the sides of an
audio cassette e.t.c.
Secondly, it has been widely used by all the levels of society; even the lower-
lower class people use audio cassettes in their daily life for their entertainment
purpose. But we generally underestimate its importance. So we thought to
pick such a topic like this to highlight its importance and its great significance.
So we thought that this is the right opportunity to let our curiosities be got
solved and we grab this opportunity to explore everything about audio
Here in this integrated term project, we have put our sincere efforts to gain all
the possible information regarding audio cassettes.
In this project we have tried to focus on the history, the evolution and working
of audio cassettes and also the ways of marketing. We have covered
designing, manufacturing, equipment, advancement in technology, customer
demands, their needs and Indian audio cassette industry’s position in the
Audio Cassette technically means a cassette containing an audio tape.
sound that can be heard
electronics or other signals of frequencies audible to humans (about
broadcasting or reception of sound
high-fidelit sound reproduction
sound recording and reproduction in general
while cassette mean a case with magnetic tape in it which is put in a tape
recorder and is used for storing and reproduction of sound.
Audio Tape on the other hand refers to a magnetic tape for recording and
playing back sound.
The First Recorders
The first recording devices were scientific instruments used to capture and
study sound waves. These devices were capable of recording voices and
other sounds long before the phonograph.
The most famous of these was Leon Scott's 1857 Phonoautograph. This
device used a horn to direct sound toward a flexible diaphragm placed at the
small end. Attached to the diaphragm was a stylus and lever assembly that
allowed the point to scratch out a line on a rotating cylinder beneath it. The
cylinder (glass strips were later used) was coated with "lampblack," probably
applied by holding it over a flame and allowing carbon to accumulate.
Below: an example of a Phonautograph tracing. A 2001 search for original
Phonautograph traces (many are published in facsimile form in books)
turned up few from the period before the invention of the phonograph. The
device probably lacked the sensitivity to record traces with enough detail to
reproduce intelligible sounds.
Alexander Graham Bell experimented with a Phonautograph in 1874, shortly
before Edison's invention. Attempting to discover how the ear detected sound,
he used a human ear (including the internal parts) from a cadaver, attaching a
stylus to the eardrum and using it to make a recording.
Bell's ear Phonautograph was a very
unusual variation on the basic technology.
The recording mechanism was the human
ear. By removing a chunk of skull including
the inner ear from a human cadaver, and
attaching a stylus to the moving parts of
the ear, he was able to use this bio-
mechanical device to make a recording of
the sounds that entered a recording horn.
It recorded on a moving glass strip, coated
with a film of carbon, so there are probably
no original recordings from it. When he
learned of the invention of the
phonograph, Bell wondered why he didn't
think of it himself.
Several researchers have investigated the possibility of using modern
technology to reproduce these pre-Edison recordings, especially following the
claim (probably false) that a recording of Lincoln's voice might exist. However,
no one has yet been successful. A small collection of original Phonautograph
recordings dating from the post-phonograph period is held by the Edison
National Historic Site, but in part due to their poor quality, a signal processing
engineer commissioned by the IEEE History Center was unable to extract any
sounds from them.
Phonographs, Graphophones, Gramophones, and so on. . .
Thomas Edison had been working on telephone equipment at the time he
conceived the phonograph. Alexander Graham Bell announced his telephone
in 1876, and many inventors set out to duplicate and improve it. Edison,
drawing on his vast experience in telegraph equipment, in July 1877
conceived of the idea of using a sensitive electromagnetic device to inscribe
telephone messages on a strip of wax-coated paper. Probably unknown to
Edison was a similar concept described in April 1877 by Frenchman Charles
Cros. The latter would later claim precedence with some justification.
A sketch of one of Edison's earliest
phonographs. A sheet of thick tinfoil,
wrapped around cylinder "C" is
indented by a stylus attached to
diaphragm "A." This hand-cranked
machine was of the type used to
demonstrate the principle. Production
models had provisions for keeping the
speed constant and other
After some experimentation, he turned instead to a device that could record
straight from the air instead of relying on a telephone connection. This line of
inquiry resulted in the construction of the first functional phonograph in early
December, 1877. He demonstrated it almost immediately in the New York
office of Scientific American magazine, and in subsequent months the
publicity the invention generated resulted in a new nickname for Edison: "The
Wizard of Menlo Park" (referring to his Menlo Park, New Jersey laboratories).
Edison did little to commercialize the phonograph himself, and a limited
number of licensees made unsuccessful attempts to sell the new device,
including a German firm that introduced a talking doll.
Within a decade, however, Edison had a new competitor in the form of the
Graphophone. Essentially an improved phonograph, the new recorder
stimulated Edison to return to his invention, and the result in 1886 was the
improved phonograph. Phonograph and graphophone licensees attempted to
lease or sell the devices to stenographers to replace hand-writing. They made
little money until someone had the bright idea to make a coin-operated
phonograph for public amusement. By supplying ready-made cylinders, they
transformed the device into an entertainment technology. Following much
legal wrangling over patents in the 1890s, Columbia Phonograph emerged as
a major competitor to the Edison company, and survives today as part of CBS
The graphophone in its original form was an
improved form of the phonograph. One main
difference, which Edison would soon adopt,
was the use of a cardboard-coated wax
cylinder instead of a sheet of tinfoil. The
exact construction of the cylinders and the
materials used changed considerably in later
years, though the basic concept of recording
into a soft, plastic material was retained.
(image from NMAH)
In 1894, Emile Berliner modified the phonograph/graphophone to use a disc
rather than a cylinder. Edison had tried and rejected this idea, but Berliner
used it in part because the core of his invention was a way to mass produce
records by stamping them out into a hard rubber material. He also avoided
infringing Edison's patents by cutting the groove into the record with a side-to-
side wiggle, rather than Edison's hill-and-dale groove. The first incompatible
format had thus been invented.
Berliner's gramophone. Although others
had considered the idea, Berliner
pushed forward with a disc record. He
made no effort to offer a device that
would record sounds, but introduced the
concept of a record player that
consumers would use for home
entertainment. Using an elaborate
process, he was able to make
duplicates of recordings in mass
quantities. The playback-only
phonograph dominated the market until
the advent of tape recorders.
An early illustration of the Berliner
system, showing a the player (top) and
Edison formed his own company to make records, while the Berliner interests
formed Victor in 1899. Through many name changes and one or two changes
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in ownership, Victor would eventually emerge as RCA-Victor in the U.S., JVC
in Japan, HMV in England, Deutsche Gramophon in Germany, and others.
Disc records made serious inroads into the phonograph market, and gradually
most companies dropped the cylinder players during and after the first decade
of the 1900s. Edison continued to produce them until his entertainment
phonograph division was closed in 1929. Victor introduced the popular
Victrola record player in 1906, marking a period when the disc record became
king and the "Victrola" brand name became virtually synonymous with record
For the home consumer, the phonograph (or, as it was often called outside
the U.S., the gramophone), was the only widely owned sound recording or
reproducing technology through the end of World War II. But in recording
studios, particularly in the radio and movie industries, times were changing.
There were numerous attempts to record sound as a visible record rather than
a groove, dating from the late 19th century. None was commercially
successful until the early 1920s, when several firms introduced sound
recording systems that recorded sound onto photographic film. They were all
intended to be used with motion pictures, which had emerged as a major
money maker in the 1910s. Thomas Edison, Western Electric, and others had
developed phonograph-based systems for adding sound to motion pictures,
but none worked well due in part to the difficulty of synchronizing the sound to
the picture. With the optical systems, the sound was recorded directly onto the
same film that held the images, so it was always in synch.
Between about 1906 and 1927, numerous "sound-on-film" optical systems
emerged, but they still had technical problems. In fact, many of the early
talkies, including the famous film The Jazz Singer of 1927, used the sound-
on-disc technology introduced by Western Electric. While perhaps the best of
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the disc systems, the Western Electric system began to be replaced by
improved sound-on-film technologies as early as 1929. Sound-on-film became
the standard way to record and reproduce sound in movies through the
1980s, and is still used some today.
An example of a "variable area" soundtrack (one of the
two major systems; the other was called "variable
density") on the right edge of a 16 mm film.
The era of the phonograph also saw the introduction of an alternative
recording technology that was little seen by the public but increasingly used in
studios. Magnetic recording, which is today used for video and audio tape,
was first introduced around 1899-1900 by the Danish inventor Valdemar
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Poulsen. Poulsen envisioned that it would be useful for office dictation and
telephone recording, but his "telegraphone," manufactured in the U.S. and
Europe by various firms, never took off. It was virtually forgotten in the U.S.,
but inventors in Germany and England persisted.
The earliest version of the
telegraphone looked a bit
like a cylinder phonograph.
For simplicity's sake, the
inventor wrapped the wire
(onto which the recording
was made) around a
cylinder. The recording
head tracked the wire
along the surface.
The advent of electronic amplifiers for the telegraphone in the 1920s and the
introduction of an oxide-coated tape in place of the solid steel wires and
bands used before resulted in steady improvements in sound quality. The
BBC, the CBC, and the RRG (the German broadcasting agency), among
others, used steel-band magnetic recorders extensively all through the 1930s.
The Dailygraph, a wire
recorder for dictation and
telephone recording, was
available for sale during
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By the end of the decade, the German companies AEG and I. G. Farben had
improved the tape recorder and its coated-plastic recording medium to the
point where it could approach the best disc recorders in sound quality. Its
ability to make very long recordings and recordings under conditions of
vibration and shock helped make the "magnetophon" popular for field and
telephone surveillance recordings as well. For radio broadcasting, the best
studio magnetophons rivaled or exceeded high quality American and British
disc recorders by the time Berlin fell in the spring of 1945.
This AEG magnetophon was
one of several versions of the
technology developed in
Germany between the early
1930s and 1945. Like modern
audio and video recorders, it
employed a plastic tape coated
with a layer of extremely fine
iron powder (modern recorders
use different mixtures of iron
and other materials).
A Chronology of Magnetic Recording
1878 - Inspired by a visit to Edison's laboratories in Menlo Park, New Jersey,
a prominent American mechanical engineer named Oberlin Smith conceived
the idea of recording the electrical signals produced by the telephone onto a
steel wire. He files a patent caveat but not a formal patent.
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1888 - Oberlin Smith, deciding that he will not pursue his idea, "donates" it to
the public by publishing his ideas about magnetic recording in the journal
1889 - Danish inventor Valdemar Poulsen re-discovers ( perhaps after seeing
Smith's article or the Tainter patents ) the principle of magnetic recording.
Over the course of the next few years he produces practical sound recorders
for steel wire and tape. He takes patents in Denmark, the United States, and
elsewhere and attempts to sell his patent rights to investors. The machine,
called the Telegraphone utilises a steel wire wound helically on a cylinder
rotating under an electromagnet connected to a carbon microphone or an
earphone. It is described as a device to record telephone messages in the
absence the called party.
1900 - Poulsen's first major demonstration of the Telegraphone takes place at
the Paris International Exhibition of 1900. The Telegraphone is desribed in
glowing terms by the technical and scientific press as superior to the
phonograph and a great advance in physics as well.
1903 - The American Telegraphone Company formed in Washington, D.C.to
manufacture the Tele graphone. A manufacturing facility in Wheeling, West
Virginia set up to make the machines, and the company makes a large public
stock offering. American Telegraphone creates several distributorships across
the country to handle service and sales. Telegraphone publicity over the next
decade or so promotes the various models of the machine as a dictation
system and an automatic telephone recorder.
1910 - American Telegraphone, failing because of bad management and
production problems, moves production to Springfield, Mass.
1911 - Lee DeForest, then working for the Federal Telegraph Company, is
asked to develop an amplifier to allow the recording of high-speed radio
telegraph messages received on a type of receiver called the Tikker. Deforest
uses his Audion tube, invented in 1907, to make his first practical electronic
amplifier. DeForest later tries to apply the amplifier and Telegraphone to the
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making of motion picture soundtracks, but the work does not result in a
1918 - American Telegraphone enters receivership after having sold only a
few hundred machines. The company remains in existence until 1944 when it
is finally disolved.
Early 1920s - German inventor/entrepreneur Curt Stille modifies the
Telegraphone to use electronic amplification and markets the patent rights to
the device, a wire recorder, to German and British companies.
1925 - Stille and another German, Karl Bauer ( a licensee of the Stille wire
recorder patents ), market an improved wire recorder telephone
answering/dictation machine called the Dailygraph. The machine was
manufactured by the Vox company, a lso of Germany. Later versions of the
Dailygraph include provisions for a cartridge, apparently the first use of a
c. 1928-29 - A British motion picture production company, Ludwig Blattner
Picture Corporation, takes a license to manfacture Stille technology. The firm
unsuccessfully tries to make and distribute movies with a synchronized
soundtrack on wire. Later machines, modified by Blattner, use steel tape
instead of wire.
Radio could be recorded from the late 1920's on machines like the huge
Blattnerphone, or the Marconi-Stille. The sound was recorded magnetically on
rapidly-spinning reels of steel wire. Editing could only happen with the aid of
wire cutters and welding equipment, so the machines were only really used to
record broadcasts for later repeats. So expensive were the machines that
wire was often re-used, rather than kept for archiving.
1930 - Bell Telephone Laboratories initiates a major research effort in
magnetic tape recording under the direction of Clarence N. Hickman. By
1931, prototypes or designs are completed for a steel tape telephone
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answering machine, a central-office message announcer, an endless loop
voice-training machine, and a portable, reel-to-reel recorder for general
purpose sound recording. None of these enter production. AT&T's official
policy on telephone recorders is that they will not be allowed on public
The German, Stille, and Marconi form the Marconi-Stille Company which
builds the first steel band recorders for the BBC: the specifications are the
following: width 3mm (1/8"), thickness: 80 cm (3x10-3 mil), speed: 1.5 m/s (60
ips), mass of a full reel: 25 kg (55 lbs); fairly dangerous use (risk of deep
cuts). 1931-32 - Blattner sells an experimental steel tape recorder to the BBC
but goes bankrupt the same year. Meanwhile, the British Marconi Wireless
Telegraph Company purchases the U.K. rights to the Stille patents. The BBC
and Marconi jointly produce several steel tape recorders and introduce them
to BBC Empire service by 1932. Similar steel tape recorders are used in radio
service in Canada, Australia, France, Egypt, Sweden, and Poland. Because
the machines depend on a special steel tape made in Sweden, supplies are
threatened when World War II begins.
AEG, a large German electrical manufacturer, purchases the patent rights of
the independent inventor Fritz Pfleumer, who after 1928 patented a system
for recording on paper coated with a magnetizable, powdered steel layer.
AEG sets about designing a tape recorder, while it collaborates with the
German chemical firm I.G.Farben to develop a suitable tape. I.G.Farben
experiments with tape coated with carbonyl iron powder, made under a
proprietary process and used in inductor cores.
c.1933-35 - Echophon company, another licensee of the Stille patents,
develops the Textophon, a dictation machine using steel wire. Echophon is
later purchased by ITT and made part of the subsidiary firm C. Lorenz, a
manufacturer of telephone equipment. C. Lorenz, with the help of engineer
Semi J. Begun, later markets a steel tape recorder that finds wide use in
European telephone authorities for telephone recording purposes and by
German radio networks for mobile recording.
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1935 - An improved AEG recorder, dubbed the "Magnetophon", is
demonstrated by recording the London Philharmonic Orchestra. The RRG (
the German radio authority ) begins to use the Magnetophon for
broadcasting, replacing the earlier C. Lorenz recorders.
1938 - S.J. Begun of C. Lorenz leaves Germany to start a new career in the
United States. In 1939 he takes a job at the Brush Development Company of
1939-44 - Sales of Magnetophons total 379 units. That figure rises to 937 by
1939-45 - At the Brush Development Company, S. J. Begun develops steel
tape and coated-paper tape recorders. Between 1942 and 1945 the company
designs and successfully sells to the military various types of recorders
utilizing plated media in the form of tapes, disks, and wire.
1941Weber and Von Braunmuhl from AEG develop the high frequency
biasing: the improvement is decisive and the "Magnetophon" becomes a
machine of excellent quality. 1945 - The Armour Research Foundation of the
Armour Institute of Technology invents an improved wire recorder. The
Institute succeeds in selling several thousand to the American army and navy,
and after the war sells licenses to dozens of American and European
manufacturers to make wire recorders.
American and British technical investigators "discover" the Magnetophon in
Luxembourg, France, and other places formerly occupied by the Germans. By
Spring, these investigators begin gathering information about the production
of tape recorders and tape, and the information is published by the U.S.
Department of Commerce. German patent rights on the technology are
seized by the U.S. Alien Property Custodian.
Former serviceman John T. Mullin demonstrates a captured Magnetophon to
the Institute of Radio Engineers. Performer Bing Crosby works with Mullin to
use the Magnetophon for radio broadcasts on ABC.
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Three former Armour Research Foundations employees start Magnecord
Corporation in Chicago to make a high quality wire recorder. Plans for the
wire recorder are soon dropped, and the group in 1949 introduces a tape
recorder, the PT-6. The corporate life of Magnecord ends in 1957 when it is
purchased by Midwestern Instruments, Inc.
1946-47 - The first Amour Research Foundation- licensed wire recorders
appear in the American market, manufactured by Pentron, Pierce Wire
Recorder company, and others. Brush Development company introduces its
Soundmirror paper tape recorder developed in 1939-40. A Brush licensee,
Amplifier Corp. of America, introduces the Magnephone tape recorder.
Minnesota Mining and Manufacturing ( later 3M Corp. ) introduces a line of
sound recording tapes, including type #100, a paper based tape, and type
#110, a plastic based tape. Type #111, a plastic based tape with an improved
oxide, becomes the industry standard.
1947 - Rangertone Inc., of New Jersey introduces a professional tape
recorder based on the Magnetophon.
1948 - Ampex corporation, using Armour Research Foundation and German
expertise and designs, produces its first professional tape recorder, the Model
1949-50 - Magnecord introduces two-channel tape recorders, and begins
making stereo recordings of music for demonstration purposes.
1948-49 - Sony Corporation begins its efforts to design a tape recorder.
1950 - The first catalog of recorded music on tape appears in the United
States. It is offered by Recording Associates company.
1951 - Bing Crosby Enterprises, the research team funded by Crosby and
headed by engineer John Mullin, demonstrate a crude video recording
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1956 - Ampex Corporation demonstrates its first video recorder, the VR1000.
The machine, which recorded only monodchrome signals takes the industry
by a storm and quickly becomes the standard.
On November 30, the first videotaped material on a TV show airs. It is
"Douglas Edwards and the News" on CBS.
1957 - Price of first commercial blank video tape offered by the 3M Corp.
listed as $307 per reel.
1958 - The same year that stereo LP's appear on the RCA-Victor label, RCA
introduces stereo tape, in a cartridge format requiring a special player. The
system flops almost immediately, though its production continues by a
licensee, Bell Sound, until 1964.
1962-64 - Phillips company of the Netherlands introduces the Compact
Cassette, a portable tape recorder using a small cartridge.
1965 - Ford and Mercury, in conjunction with Motorola and RCA-Victor
records, introduce the "Stereo-8" (or "eight track" ) format tape players as an
option on certain luxury models. The medium becomes the first truly
successful form of recorded music on tape in the consumer market. 8-track
tapes discontinued around 1980.
1969-70 - DuPont and BASF begin offering chromium dioxide recording
1970 - Sony introduces the U-Matic videotape recorder. The format does not
succeed well as a consumer product, but achieves great success in schools
and television stations.
1975 - Sony introduces the Betamax home video system. By using a
convenient cartridge and offering the product at a low cost, Beta quickly takes
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1976- Panasonic and JVC introduce a competitor to Betamax, the Video
Home System ( VHS ) system.
1978 - Sony introduces the first digital recorders. These were professional,
open reel PCM recorders for the studio.
1984 - Sales of recorded compact cassettes (audio cassettes) exceed LP
sales for the first time.
The Era of Tape Recording
Despite its quiet start, it was tape recording that would eventually displace
both the phonograph and optical recording methods. Eventually. Captured
German recorders were widely copied, improved upon, and re-introduced by
Ampex, EMI, and other firms in the late 1940s. Engineers used to editing
optical film found it easy to learn to edit tape, and tape represented real
improvements over optical recording in terms of convenience and low cost. In
radio, record, and movie studios, tape was almost universally adopted by the
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The first consumer magnetic recorders also appeared in this period.
Inexpensive wire recorders, developed more-or-less independently of the
Europeans, were introduced around 1946 and proved to be a short-lived hit.
When the first cheap tape recorders appeared around 1948, they quickly stole
the market. Millions of them were sold during the 1950s as part of a boom in
"hi-fi," although many owners reported that they made little use of them.
Record companies were willing to sell recorded tapes, but they could not
compete in price with records, especially the LP record introduced in 1948 by
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The popular Webster-
Chicago wire recorder, sold
from about 1946 to 1952.
Studio Tricks and Stereo
The advent of tape recorders in recording studios led to innovations in
recording that radically altered the making of music. Most radio and record
studios in the U.S. adopted Ampex recorders (although there were
competitors from RCA, Presto, and others) for making master recordings. The
less-expensive Magnecorders were popular in radio stations and studios
where these workhorse machines were used for heavy production and editing
work. The basic techniques of editing - cutting and splicing to remove, re-
arrange, or compile pieces of recordings, mixing two or more sound sources
into one recording, and fading sound in or out-were all innovations that were
made easier with tape. Where in the past performers had to execute songs
perfectly (or with minimal errors), or else face remaking the whole recording,
now it was sometimes possible to splice together two or more flawed
recordings to make a perfect one. Engineers and artists found that it was also
easier to manipulate sounds on tape, leading to the use of all sorts of special
effects, such as using a recorder to allow a single artist appear to accompany
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Once stereo recordings
were mixed down onto
a master tape, they
were recorded onto a
blank using a cutter
modified for stereo,
such as this one made
by Westrex (successor
to Western Electric's
Products Inc., or ERPI)
Even in the late 1940s, there were experiments with multitrack recording on
tape. Multiple simultaneous soundtracks had been possible, though
expensive, since the 1930s on motion picture film. As engineers reduced the
size of tape recorder heads, it became possible to mount two or three heads
on a single recorder, equip each with a recording/reproducing amplifier, and
record multiple simultaneous tracks on a single tape. This feature was used in
two ways. In the studio, groups of musicians or singers could be separated
into two or three groups, such as recording the rhythm section and the rest of
the band separately. If there was a flub on one or the other tracks, it could be
re-recorded without re-assembling the whole band. After years of perfecting
this technique, it became the basis of increasingly complex recordings in the
1960s. More and more tracks were added to recorders to allow 24 or more
tracks to be recorded on a single, very wide tape.
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Stereo in the home.
The second outcome of the use of multitrack recordings was the most evident
to the consumer; the advent of stereo sound. Engineers in the 1930s had
discovered that a two-channel (or more) recording, utilizing two microphones,
two amplifiers, and two loudspeakers, gave aurally pleasing results. The
"stereo effect" as it was called was often described as "realistic," because
human hearing has the capacity to identify the location of a sound source
based on the slight time delay in the reception of sound in each ear. In the
1950s, engineers found that the stereo effect is false-the original location of
the instruments in the studio is not perfectly simulated when a stereo
recording is reproduced. However, most listeners prefer the three-
dimensionality of the stereo effect, and it proved to be very popular. However,
it required that consumers, like studio engineers, purchase equipment that
could play stereo records, along with two-channel amplifiers and a second
The first stereo recordings available to the public were in the form of reel-to-
reel tape. Recorder manufacturers offered add-on stereo tape heads and off
board amplifiers that could be added to existing recorders. Stereo recorders
with a second head mounted next to the main head soon appeared. Almost
simultaneously, tape recorders with two miniaturized, stacked heads mounted
in the same housing appeared; tapes for these recorders were incompatible
with the earlier "staggered" head recorders. Then in 1957-8 RCA introduced a
recorder with a super-compact tape head that stacked four heads in the place
of just two, allowing a stereo tape to be flipped over and played on both sides
like a mono tape. These new "four track" tapes could not be played on either
of the other two stereo systems. This lack of compatibility, combined with the
high price of stereo tapes, discouraged sales. Meanwhile, another division of
RCA introduced the stereo LP record, also in 1957-8, along with moderately
priced stereo phonographs (stereo 45-rpm discs soon followed). Stereo LPs
could not be played on monophonic players, so for many years mono and
stereo versions of the same recordings were available. During the 1960s,
most record companies discontinued mono LPs.
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The RCA tape cartridge,
which looked like a very
large cassette, was the first
mass-market stereo tape
system in the U.S.
However, it appeared the
same year as RCA's stereo
disc, and the tape system
was not well supported by
RCA's marketing or record
divisions. It would live on for
many more years in the
field. Educational versions
of the records and tapes
were available perhaps as
late as 1970.
The Rise of the 8-track
The 8-track was a distinctively American achievement in audio, reflecting the
well-known fascination with automobiles in the U.S.. Automotive record
players, some of questionable utility, were available as original equipment or
aftermarket add-ons from about 1958 to the mid-1960s. They never sold in
great numbers, and were eclipsed by the advent of automotive tape systems.
Small cartridge tape systems appeared in the middle 1950s as a variation of
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the "cart" system that came to be widely used for spot announcements in
radio stations. This was based on an endless loop tape cartridge that had a
long playback time (over two hours was possible).
In the early 60s, an entrepreneur in California created a minor sensation with
his "Stereo-Pak" auto tape system, and this was modified and reintroduced in
a few years as the Learjet Stereo-8. Made by the same firm that made Learjet
airplanes, it was first installed in Ford cars in 1965. Soon all the American
auto makers offered this technology as optional equipment, and home and
portable versions of the players appeared. The 8-track took a large proportion
of the music market in the late 1960s and peaked in the mid-1970s. Although
it was a compromise in terms of sound quality, it required only one hand and
minimal accuracy to insert into or remove from the players, which themselves
were designed for extreme simplicity of operation. Once in the machine, the
tape played automatically and required no rewinding. In terms of responsible
engineering, the 8-track's design was a wise attempt at avoiding the
introduction of an accessory that distracted the driver. At the end of its life in
the early 1980s, it became the butt of jokes; a symbol of obsolescence and
An ascot, a convertible, and a
copy of the Sound of Music on
8-track was all it took to score
big back in those days.
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The cassette actually predated the 8-track by about a year, although it was
cheap children's technology through the late 1960s. This small, two-reel
cartridge was introduced by Phillips in Europe and Norelco in the U.S. It was
based on, but intended for a different market than a similar small cartridge
system that Phillips introduced for office dictation purposes. The "Carry-
Corder" battery operated recorder/player made low quality recordings in mono
only, but once prices for the recorders came down it proved to be a huge hit
To overcome its sonic deficiencies, engineer Ray Dolby adapted his hiss
reduction technology, versions of which appeared in pro and reel-to-reel
recorders, for cassettes in 1968-9. The introduction of better quality home
cassette decks by Ampex and others in the late 1960s and early 1970s
elevated the reputation of the format and helped make it acceptable to the hi-fi
crowd. Meanwhile it had become the technology of choice for those interested
in making copies of records for use in battery operated portables or in-car
tape players. In terms of pre-recorded cassettes, sales overtook 8-tracks in
the mid-1970s, then overtook LPs in the early 1980s. For a time in the 1980s,
the cassette was the most popular home music format for both home
recording and pre-recorded listening applications. Improved versions of Dolby
appeared tailored for tape, and the venerable gamma-ferric oxide tape
formulation, used since the 1940s for reel-to-reel tape, was superseded with
mixtures that contained iron oxide mixed with or replaced by chromium
dioxide or metal particles. The 90-minute tape became the best-selling blank
tape, reflecting the fact that two full albums could usually be recorded on a
single 90-minute cassette.
The format spawned an ever-wider variety of portable and home recorders
and players. In addition to the small battery operated portables available since
the beginning, larger, more powerful "boomboxes" (also known by a number
of other more offensive names, many reflecting the association of boomboxes
with urban African-Americans, such as ghetto blasters, n****r boxes, or even
28 | P a g e
the Third World Briefcase). In reality, the boombox was a mass market,
international phenomenon not associated with any particular race or
nationality. These versatile devices were for most Americans at least the
primary form of home audio technology, and some were even equipped with
If the trend in boomboxes was toward bulkier and bulkier devices, the
cassette spawned a second movement toward "personal audio." Following on
the heels of its successful line of home VCRs, Sony Corporation in 1977-8
introduced its Walkman line of battery operated radios and tape players.
Copycats jumped into the market the next year, and soon there was a
bewildering variety of personal audio products. The CD-walkman was
available by mid-decade, and the trend persists today with small MP3 players.
The Wire Recorder
Interest in wire recorders is growing; people too young to remember this
technology are rediscovering them at garage sales and flea markets.
Collectors are beginning to seek them out.
Unfortunately, not much reliable historical information out there about these
machines. It's a common assumption that wire recorders "evolved" into tape
recorders. On the contrary, tape, wire, and disk magnetic recorders were
invented virtually simultaneously.
These various formats were developed and promoted by different companies
or inventors, and for a while after World War II, wire recorders and tape
recorders competed in the marketplace. Why did tape win? There's no simple
answer, but you can read for yourself about rise and fall of this intriguing and
nearly forgotten form of sound recording.
Between about 1898 and 1900, Danish inventor Valdemar Poulsen
developed and patented the"Telegraphone," a telephone recorder utilizing
steel wire. The Telegraphone (pronounced with the emphasis on the second
29 | P a g e
syllable) was the first device capable of recording sound magnetically. Within
a short time, Poulsen also demonstrated a steel tape recorder and a machine
to record magnetically on a steel disk. All three types were promoted as
alternatives to phonograph-type dictating machines, or as telephone recording
However, the only type of Telegraphone that was produced in quantity used
steel wire. It was manufactured in at least two versions, one by Poulsen's
workers in Denmark, and another by the American Telegraphone Company of
Wheeling, West Virginia and later Springfield, Massachusetts.
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Even though the wire recorder was still in its infancy, the technology that
would bring about its obsolescence was already taking shape. AEG, a
German electrical manufacturer, and I.G. Farben, a large German chemical
firm, teamed in the early 1930s up to design a tape recorder that used a new
type of tape. Rather than the solid steel band introduced by Poulsen,
engineers developed a new medium consisting of a special iron oxide powder
coated onto a plastic tape (there were other variations, such mixing the iron
into the liquid plastic and then casting the homogenous mixture into a thin
tape). The recorder, called the Magnetophon was initially disappointing in its
performance compared to existing magnetic recorders, but with numerous
improvements it soon became the standard in all German RRG radio stations.
It was discovered during the war by the Allies and after Germany fell in early
1945, many examples are "liberated."
31 | P a g e
One form of
By 1945 Brush had on the market a tape recorder, the "Soundmirror,"
somewhat like the German Magnetophon. But it was still not clear that tape
was superior. Brush also introduced a wire recorder at about the same time.
Based on wartime research, the Brush recorder used a special plated wire
made of a bronze core surrounded by steel plating.
A Brush model
recorder of the
early 1950s. This
at over $500, was
expensive on the
market at the
32 | P a g e
Meanwhile, Armour Research Foundation had received a contract from the
United States Navy to develop a portable sound recorder. The original
recorder was modified make it more rugged. Between 1942 and the end of the
war, Armour and a licensed manufacturer, General Electric, have made
perhaps a few thousand of these recorders. They were used for many
purposes throughout the war, most notably as a portable field recorder for
33 | P a g e
Beginning in 1945, Armour Research Foundation shifted from war production
to selling licenses. The Foundation licensed the manufacture of its recorders
to over a dozen American and European manufacturers, and introduced a
cheaper "consumer" design which many of the licensees adopted. The
resulting income funded additional research that Armour hoped would help
the organization remain at the forefront of the industry. Armour standards for
wire speed, the wire itself, wire reels, and other basic features are adopted by
nearly all manufacturers. Brush recorders were also on the market by 1946,
but Brush with few exceptions was unable or unwilling to license its designs.
Lawyers for Brush and Armour would eventually work out a cross-licensing
agreement between the two, but neither group benefited much from it.
Wire recorders never approached the sales of other electronic devices of the
day such as televisions and radios, and went into sharp decline after 1954. In
the 1954-55 retail "season," high fidelity equipment became a big seller. While
tape recorders (which also suffered from relatively slow sales through the
1950s) became part of the hi-fi phenomenon, wire recorders faded into
obscurity. Why did the home wire recorders of the postwar period fail? My
theory is that 1) designers of wire recorders aimed at the mass market rather
than the professional market, and this led to the perception that wire recording
was second-rate, especially compared to tape recording; 2) record companies
failed to embrace the new technology, leaving consumers with no pre-
recorded wires and hence fewer ways to enjoy the wire recorder; 3) the
Armour-designed wire recorders were difficult to use and unreliable. They had
the annoying tendency to snarl wires, and the wire was so fine that handling it
could be aggravating; and 4)after the LP record appeared in 1948/9 with
massive corporate support, it was more difficult to convince consumers that
wire recorders would be the next big thing.
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A History of the Eight Track Tape
The Eight Track tape recording system was popular from 1965 to the late
1970s. While today it has become an icon of obsolescence, it was a great
commercial success and paved the way for all sorts of innovations in portable
listening. The eight track tape consisted of an endless loop of standard 1/4-
inch magnetic tape, housed in a plastic cartridge. On the tape were eight
parallel soundtracks, corresponding to four stereo programs. For many people
old enough to have owned an eight track system, it is a technology associated
with the automobile and in-car listening. Ironically, however, it was first
developed not by the auto industry, but by a leading aircraft manufacturer.
Years before he set down to work on the famous Learjet, William Powell Lear
had made a name for himself developing instruments and communications
equipment for airplanes. In 1945, Lear Inc. was moving into the consumer
electronics field. The company became a licensee of a Chicago-based R&D
laboratory called the Armour Research Foundation allowing Bill Lear access
to Armour's successful wire recording technology, bits of which made their
way into his own design for an endless loop wire recorder. The advantage of
using an endless loop is that it can easily be built into a self-contained
cartridge, plus it does not require rewinding. However, it is not clear whether
the wire recorder actually offered by the Lear company used an endless loop.
It appears to have used a two-reel system enclosed in a cartridge.
Lear posed with his wire
combination set in early
1945. The wire
"magazine" he holds can
record up to one hour.
35 | P a g e
This may have been the genesis of Lear's interest in endless loop technology,
but Lear's early experiments did not lead directly to the 8-track. Instead, Lear
dropped the project to concentrate his efforts on aircraft.
An ad for
Some time after 1950, Bernard Cousino, the owner of an Audio Visual
equipment and service company called Cousino Electronics in Toledo, Ohio,
became interested in endless loop sound recordings. He won a small contract
to build a "point of sale" audio device-- that is, a store display that played a
recorded message over and over endlessly. The difficulties of using an
automatic phonograph to accomplish this suggested that some other medium
might work better. Cousino, aware of the widespread use of short motion
picture film loops for similar purposes, began experimenting with an 8-
millimeter endless loop film cartridge marketed by Television Associates, Inc.
of New Hampshire (a maker of antennas).
36 | P a g e
In the mean time, another inventor named George Eash designed and
patented a similar cartridge that came to be known as the "Fidelipac." Eash
was an inventor whose main claim to fame before the Fidelipac was a patent
for a helmet-mounted loudspeaker for soldiers. Like Cousino, he was from
Toledo and was interested in the audio-visual field. He became interested in
cartridges after he began to rent a work space in the Cousino Electronics
building. Eash designed and patented a cartridge with specifications similar to
the Echomatic, later modifying it to include a more complex reel braking
mechanism. But while Cousino had assembled and marketed his own
products, Eash chose to license his designs to a outside manufacturers. One
result of this strategy was the widespread adoption of the Eash cartridge
standard by a range of different companies. Most of these companies were
interested in making background music systems to compete with Muzak
(which at that time was usually distributed via cable or, in some areas, FM
radio). Eash-type cartridges could hold several hours of recorded
programming, and once playing they would continue to play continuously.
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Eash's cartridge, although complex internally and prone to failure, was
nonetheless the basis of dozens of other commercial applications of the
endless loop, two of which were particularly successful. The first and most
long-lasting was in broadcasting. Radio equipment manufacturers since the
end of World War II had been developing equipment to automate radio
stations-- the idea was to replace expensive d.j.'s and board operators with
machines. Eash's design became the basis of several new systems adapted
for radio station use, with heavy duty mechanisms, automatic starting and
stopping features and end-of-tape sensors. Even in the early 1960s, many
radio stations had put some or all of their music, spot announcements, and
station IDs on carts that could be quickly inserted and played and which could
be automatically stopped at the beginning of the recording.
38 | P a g e
An early ATC (Automatic Tape
Control) Corp. recorder/player
for the Fidelipac cartridge
based on Eash patents.
Because Fidelipac cartridges
originally came in three sizes,
the recorder featured a wide
slot. However, most radio
stations adopted the smallest
Fidelipac also promoted the idea of using its endless loop technology in the
automobile, but did little to address the issue of just what people might listen
39 | P a g e
although it is
not clear how
Suddenly Bill Lear appeared on the scene, newly world famous for his
spectacularly-successful Learjet business plane, and announced in 1965 that
he had developed a cartridge with eight tracks that promised to lower the
price of recorded tapes without any sacrifice in music quality. In 1963,he
became a distributor for Muntz Electronics, mainly in order to install 4-track
units aboard his Learjets. Dissatisfied with the Muntz technology, he
contacted two of the leading suppliers of original equipment tape heads, the
Nortronics Company and Michigan Magnetics. He specified a head with much
40 | P a g e
thinner "pole-pieces" and a new spacing that would allow two tracks (or one
stereo program) to be picked off a quarter-inch tape that held a total of 8-
tracks. Although a departure from the Muntz player, the technology of the
closely-stacked multitrack head was by the early 1960s well established in
fields like data recording. Lear in 1963 developed a new version of the
Fidelipac cartridge with somewhat fewer parts and an integral pressure roller.
During 1964, Lear's aircraft company constructed 100 "Stereo-8" players for
distribution to executives at the auto companies and RCA.
The earliest Ford 8-track
players were designed for a
minimum of controls and
extreme simplicity of
operation--the point was
the keep the driver's eyes
on the road, not on the
Just how Bill Lear managed to convince the auto executives to cram those
players under the dashboards of Ford Mustangs and Fairlanes is a little
unclear. Certainly Lear brought his reputation as the successful leader of a
business, and had many personal contacts in industry. In a roundabout kind of
way, he already had ties to Ford. In the 1930s Lear and Paul Galvin had
together built Motorola into a leading manufacturer of car radios, and Motorola
was now affiliated with Ford.
Whatever the details of Lear's selling job, the keys to the Stereo-8's
spectacular success seems to have been linked to getting the backing of both
Ford and the recording industry. After getting RCA Victor to commit to the
mass-production of its catalog on Learjet Stereo-8 cartridges, Ford agreed to
offer the players as optional equipment on 1966 models. The response, in one
41 | P a g e
Ford spokesman's words, "was more than anyone expected." 65,000 of the
players were installed that year alone. The machines were initially
manufactured Ford's electronics supplier and the firm that had pioneered the
"motor victrola" --Motorola.
console of a
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Various Raw Materials used in audio cassettes are as under :
1. Base Film
2. Iron Oxide
6. Wetting Agents
7. Dispersing Agents
8. Lubricating Agents
9. Anti-static Compounds
10. Polyethykene terephthalate
44 | P a g e
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Different uses or applications of audio cassettes are as under
Home and Public Entertainment :- First of all audio cassettes are
used for entertainment. Music of different types are stored on the music
tapes and is played for both home and public entertainment. Music of
all types whether Indian or western, pop or rock, classical or hip hop,
all are available on the cassettes. Also devotional songs, sayings of
holy persons are also stored (recorded) on the cassettes and are heard
by the people.
Audio Broadcasting by Radio Channels :- Audio cassettes are also
used for broadcasting of music, interviews, repeated commentary or
repeated news by radio channels. Now a days CD’s and computers
have started replacing the audio cassettes because of their better
performance but it is still used in some broadcasting agencies.
Cockpit Voice Recording on Aircrafts :- Audio cassettes are also
used for the recording of voice of the crew members on board. These
cassettes are kept in a special kind of container and thus does not get
damaged even in case of a plane crash and thus provides the last
minute communication held between the pilot and his crew. This
sometimes help in knowing the cause of the crash.
Sound Recording in Film Industry :- Audio cassettes are also used
for recording the sound i.e music of various movies in the film industry.
Sound Recording Studios :- Audio cassettes are also used in the
sound recording studios. These studios keeps a copy of the cassette
and uses it for duplication or making other cassettes.
46 | P a g e
Answering Machines :- Audio cassettes are an important part of the
answering machines. The message left the person on the other side is
automatically stored on the cassette and can be played back later on.
Magnetography :- Audio cassettes are also used in the field of
Education : Cassettes are also used for education purposes. They are
used for teaching various things like one learns in a school or college.
Machine Tool Control :- Special instructions are given to the workers
about the handeling of the machine tools by usig the audio cassettes.
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COMPACT AUDIO CASSETTE
The compact audio cassette audio storage medium was introduced by Philips
in 1963. It consists of a length of magnetic tape from BASF inside a protective
plastic shell. Four tracks are available on the tape, giving two stereo tracks –
one for playing with the cassette inserted with its 'A' side up, and the other
with the 'B' side up, thus mimicking gramophone records. There were other
magnetic tape cartridge systems at the time, but the compact cassette
succeeded through Philips's backing. The mass production of compact audio
cassettes began in 1965 in Hanover, Germany, as did commercial sales of
prerecorded music cassettes, known as music cassettes or MC for short.
The cassette was a massive step forward in convenience from reel-to-reel
audio tape recording, though the limitations of the cassette's size and speed
compared poorly in quality. Unlike the open reel format, the two stereo tracks
lie adjacent to each other rather than a 1/3 and 2/4 arrangement. This
permitted monaural cassette players to play stereo recordings in a highly-
compatible "summed" form and permitted stereo players to play mono
recordings through both speakers. The tape is 1/8 inch (3.175 mm) wide, with
each stereo track being 1/32 inch (0.79 mm) wide and moves at 17/8 inches
per second (47.625 mm/s). For comparison, the typical open reel format was
¼ inch (6.35 mm) wide, each stereo track being 1/16 inch (1.5875 mm) wide,
and running at either 3¾ or 7½ inches per second (95.25 or 190.5 mm/s).
Some machines did use 17/8 inches per second (47.625 mm/s) but the quality
The original magnetic material was based on ferrite (Fe2O3), but then
chromium dioxide (CrO2) and more exotic materials were used in order to
improve sound quality to try to match those of vinyl records. These had
different bias requirements, requiring more complicated equipment.
A variety of noise reduction schemes were used to increase fidelity, Dolby B
being almost universal for both prerecorded tapes and home recording. By the
48 | P a g e
late 1980s, sound fidelity on equipment by manufacturers such as Nakamichi,
ReVox and Tandberg far surpassed the levels expected of the medium by
early detractors and on suitable audio equipment could challenge the sound
quality of the compact disc.
Tape length was usually measured in minutes total playing time, and the most
popular varieties were C46 (23 minutes per side), C60 (30 minutes per side),
C90, and C120 (usually thinner tape, more likely to be destroyed in use).
Some vendors were more generous than others, providing 132 meters or 135
meters rather than 129 meters of tape for a C90 cassette. C180 and even
C240 tapes were available at one time, but these were extremely thin and
fragile and suffered badly from effects such as print-through which made them
unsuitable for general use. There was also a C-100, which could
accommodate a 50 minute album on each side – a possible factor in its
The cassette had originally been intended for use in dictation machines, but
quickly became a medium for distributing prerecorded music – particularly
through Philips's record company, PolyGram – with an option for home
recording use. Cassettes were also used for purposes such as journalism,
field history, meeting transcripts and so on. In the 1980s, Tascam introduced
the Portastudio, a four-track recorder for home studio use, which increased
the audio quality possible on cassette by doubling the tape speed and using
DBX noise reduction (which worked by compression to increase the dynamic
Most cassettes were sold blank and used for recording the owner's records
(as backup or to make compilations), their friends' records or music from the
radio. This practice was condemned by the music industry with such slogans
as "Home taping is killing music". However, many claimed that the medium
was ideal for spreading new music and would increase sales, and strongly
defended at least their right to copy their own records onto tape. In the late
1970s, Sony brought out the Walkman, a small portable cassette player,
which greatly increased the consumption of music in this manner. Cassettes
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were also a boon to people wishing to make bootlegs (unauthorized concert
recordings) for sale or trade.
Cassettes can be played on a wide variety of different types of device. Early
recorders tended to be small battery-powered portable devices, in keeping
with the intention of the medium for dictation, reportage and similar low-level
recording duties, but by the mid 1970s, the cassette deck became a
commonplace component of home high fidelity systems, largely superseding
the reel-to-reel recorder for home use. Another key element of the cassette's
success was its use in in car entertainment systems, where the small size of
the tape was significantly more convenient than the competing 8-track
cartridge system. Cassette players in cars and for home use were often
integrated with a radio receiver, and the term "casseiver" was occasionally
used for combination units for home use. In-car cassette players were the first
to adopt the idea of automatic reversal of the tape at each end, allowing a
cassette to be played endlessly without manual intervention. Home cassette
decks soon followed this practice as well.
Many home computers of the 1980s, notably the TRS-80, Commodore 64, ZX
Spectrum, Amstrad CPC and BBC Micro, used cassettes as a cheap
alternative to floppy disks as a storage medium for programs and data. Data
rates were typically 500 to 2000 bit/s, although some games used special
faster loading routines, up to around 4000 bit/s. A rate of 2000 bit/s equates to
a capacity of around 660 kilobytes per side of a 90 minute tape.
Technical development of the cassette effectively ceased when digital
recordable media such as DAT and MiniDisc were introduced in 1992. Philips
attempted to introduce the Digital Compact Cassette – a DAT-like tape in the
same form factor – but it failed in the market. Since the rise of cheap CD-R
discs, the phenomenon of "home taping" has effectively switched to compact
50 | P a g e
DIGITAL AUDIO TAPE
Digital Audio Tape (DAT or R-DAT) is a signal recording and playback
medium introduced by Sony in 1987. In appearance it is similar to a compact
audio cassette, using 4 mm magnetic tape enclosed in a protective shell, but
is roughly half the size at 73 mm × 54 mm × 10.5 mm. As the name suggests
the recording is digital rather than analog, DAT converting and recording at
higher, equal or lower sampling rates than a CD (48, 44.1 or 32 kHz sampling
rate, and 16 bits quantization) without data compression. This means that the
entire input signal is retained. If a digital source is copied then the DAT will
produce an exact clone, unlike other digital media such as Digital Compact
Cassette or MiniDisc, both of which use lossy data compression.
The technology of DAT is closely based on that of video recorders, using a
rotating head and helical scan to record data. This, crucially or not, prevents
DATs from being physically edited, as ProDigi, DASH, or analogue tape
recordings can be.
The DAT standard allows for four sampling modes: 32 kHz at 12 bits, and 32
kHz, 44.1 kHz or 48 kHz at 16 bits. Certain recorders operate outside the
specification, allowing recording at 96 kHz and 24 bits (HHS). Some machines
aimed at the domestic market did not operate at 44.1 kHz when recording
from analog sources. Since each recording standard uses the same tape the
quality of the sampling has a direct relation to the duration of the recording -
32 kHz at 12 bits will allow six hours of recording onto a three hour tape while
HHS will only give 90 minutes from a three hour tape. Included in the signal
data are subcodes to indicate the start and end of tracks or to skip a section
entirely, this allows for indexing and fast seeking. The tapes themselves are
not physically editable in the cut-and-splice manner of analogue tapes. Two
channel stereo recording is supported under all sampling rates and bit depths,
but the R-DAT standard does support 4-channel recording at 32 kHz.
51 | P a g e
DAT tapes are between 15 and 180 minutes in length, a 120 minute tape
being 60 meters in length. DAT tapes longer than 60 meters tend to be
problematic in DAT recorders due to the thinner media.
The format was designed for audio use, but through the ISO DDS standard it
has been adopted for general data storage, storing from 1.3 to 72 GB on a 60
to 170 meter tape depending on the standard and compression. It is,
naturally, sequential-access media and is commonly used for backups. Due to
the higher requirements for integrity in data backups, a computer-grade DAT
DAT was not the first digital audio tape; an early form known as pulse-code
modulation (PCM) was used in Japan to produce analog phonograph records
in the early 1970s, but it was not developed into a consumer product.
Likewise, DCC was not a success either. Modern DAT has not been very
popular outside of professional and semi-professional music artists, although
the prospect of perfect digital copies of copyrighted material was sufficient for
the music industry in the US to force the passage of the Audio Home
Recording Act of 1992, the so-called DAT Tax. The inclusion of SCMS (Serial
Copy Management System) in DAT recorders, to prevent digital copying for
more than a single generation, was another response.
Flaws on the tape or heads can cause the signal to mute briefly on playback,
which can be frustrating when attempting to copy material.
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DIGITAL COMPACT CASSETTE
DCC is a medium on which audio information
is digitally encoded and which reproduces CD
quality sound. Since it uses the standardised
format of analogue cassettes, it is completely
compatible with analogue cassette decks.
Text mode allows a DCC deck to display support information (eg track title,
artist name) in several different languages, about the recordings on the tape.
The styling has been improved: the DCC tape has a slide off cover which
makes access easier, plus the front is completely smooth and suitable for
album art. The DCC cassette is protected from dirt and wear by a sliding door,
so that the cassette will not easily become jammed or tangled.
DCC introduces a real breakthrough: PASC. PASC is precise and efficient. It
compresses the data so that it can be accommodated on standard length
audio tape. PASC ensures only sounds within the hearing threshold and takes
into account the fact that loud sounds mask soft ones.
DCC tape frames contain PASC information in a checkerboard pattern, which
stops drop-outs impairing the quality of the sound performance. DCC has all
of the error correction possibilities of compact disc.
Azimuth is the position and angle of the tape in relation to the head. In
conjunction with the Fixed Azimuth Tape Guidance (FATG) mechanism fitted
to the DCC head assembly, the Azimuth Locking Pins (ALPs) ensure not only
improved wrap-around tape-to-head contact, but also consistent azimuth
To play back information in the DCC miniature track dimensions, DCC uses
magneto-resistive (MR) technology. MR technology is a major advance in the
thin-film head for digital playback. MR's high-read sensitivity allows narrower
tracks to be used for digital coding, so that overall tape data density is
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DCC takes the best of years of analogue cassette development, and adds the
perfect sound of digital technology.
In the Eighties, a Philips invention captured the limelight. Compact Disc
opened a new era of digital, perfect sound. Digital audio in the CD format
offers high dynamic range and very low noise, as well as low distortion, wide
channel separation and total absence of wow and flutter: in a word, natural
sound. Digital audio also offers extra user convenience with fast track access
and programming. The error correction process in the CD player corrects any
mistakes from slightly soiled or damaged CDs, so that the recordings retain
their original purity. Consumers recognise this and the CD has become
Yet in the Nineties another Philips invention has centre-stage: Digital
Compact Cassette, (DCC). DCC is the marriage of compact cassette to Digital
Audio, forming a union that combines perfect sound and high convenience
with even greater versatility.
With the latest advances in digital audio technology, it has become possible to
record digital-quality sound on a new type of audio cassette, which runs at
normal compact cassette speed. With its revolutionary and extremely efficient
PASC coding (see below), DCC achieves up to 18-bit resolution, producing
superb digital sound of Compact Disc quality. DCC uses digital technology to
produce digital quality on tape. And DCC will playback standard analogue
tapes. In this chapter, we will look at several aspects of DCC and we will
examine PASC coding. We will also look into the new head assembly which is
a key to the DCC design. Finally, we will discuss the mechanical parts of the
54 | P a g e
Important aspects of DCC
DCC operating convenience is well up to CD standards, especially with pre-
A number of features has been incorporated in DCC tapes and decks.
Track and time codes are on the tape. These codes, combined with
autoreverse, make track access effortless and fast. DCC decks can locate a
chosen track on either side of the tape.
A brand new feature of pre-recorded DCC is text mode. Text mode allows
cassette decks to display support information about the recordings on the
tape, such as album title, a complete list of track titles, names of the artists on
each track, and lyrics (displayed in sync with the music). Television screens or
remote control units can be connected to the cassette deck to display more
extensive information. Text can be written on the tape in up to seven
The well-known durability of cassettes is enhanced in DCC by digital error
correction, improved mechanical design and built-in tape protection. As for
styling, the new DCC design, which is smoother and slimmer, features an
integral cover design, which has more visual appeal, and is easier to handle,
carry and store.
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In addition, DCC decks
have a unique and
they are compatible with
Customers can play
their current analogue
cassette collection on
their DCC deck. DCC is
available to the
customer as a total
including decks from a
range of manufacturers,
and blank cassettes as
well as cassettes pre-
recorded on leading
Figure 2 Only one generation of digital to digital
Numerous digital first copying is permitted
generation copies on to
DCC blank tape can be
made from an original,
pre-recorded DCC. But,
any further copies (ie
2nd, 3rd etc generation)
made from the first
generation copy will not
Autoreverse is a standard feature of DCC decks, which allows continuous
listening to both sides of an analogue or a DCC tape.
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All these factors make DCC the logical, digital successor to Compact
Cassette. It meets higher demands for sound quality, durability and style. It is
designed for the new generation of music lovers in a new digital age.
A number of design features of the DCC cassette improve upon its analogue
The cassette is smooth on the top side, which can now be used for artwork or
information. This is because the drive hub openings are only needed on one
side of the cassette (as autoreverse is standard on DCC).
The tape and tape drive wheels, which are exposed in the analogue version,
are concealed in DCC cassettes by a metal sliding panel called a slider. This
slider, which is pushed aside automatically when the cassette is loaded, also
locks the tape hubs. This means that:
the tape is protected against soiling and scratches
the tape does not tangle, unwind or jam
cassettes can be carried around safely without their cases.
DCC cassettes are provided with cases, which provide additional protection
for the cassette and space for extra information such as a booklet. The case
is in the form of a slide-out sleeve which allows the smooth side of the tape to
be visible (eg to display artwork) and facilitates easy access to the cassette.
The DCC cassette is made of new materials which are specified for use over
a wider temperature range than those of the analogue cassette. The length of
a blank DCC cassette can be indicated by holes in the rear of the housing.
These enable DCC decks to calculate and to display the time on the cassette.
Accidentally writing over a recording can be prevented by a record protection
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The tape is a standard videochrome tape: chromium dioxide- or cobalt- doped
ferric-oxide, 3-4 µm thick in a total tape thickness of 12 µm. As in analogue
cassettes, the tape is 3.78 mm wide, and is bi-directional. This format reduces
access time, since less tape needs to be wound. It also allows continuous
DCC uses PASC (Precision Adaptive Sub-band Coding), a newly developed
system which compresses the audio information so that it will fit on an
audiotape and produce CD sound quality.
How does PASC do this? PASC concentrates on maximising the efficiency of
the digital coding, by taking into account two factors not previously considered
in digital audio:
1. The ear hears only sounds above a certain loudness (dB) level, called
the hearing threshold. The threshold of hearing depends on the
frequency of the sound (since the ear is more sensitive to mid- range
frequencies) and on the individual. Consequently, it is only necessary
to record sound above the hearing threshold, provided that the
threshold is taken as the reference for both recording and playback.
Figure 4 The ear hears only sounds above a certain level, called
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2. Louder sounds hide (mask) softer sounds. A whisper, perfectly audible
in a quiet room, will not be heard in a busy street. In fact, louder
sounds dynamically adjust the threshold of hearing. With computer
techniques, it is possible to track this threshold adjustment, making it
necessary for only the sounds above this dynamic threshold to be
recorded. Of course, this applies to both recording and playback.
Figure 5 Louder sounds mask softer sounds.
PASC achieves very efficient sound recording indeed. It needs only one
quarter of the bit rate of PCM (of CD). This level of efficiency creates
adequate room for precise recording of what the ear actually hears. The
sound quality of DCC is in every way comparable with Compact Disc.
More information on how PASC coding works can be found in the Appendix.
Tracks and tape frames
DCC signals are recorded on nine parallel tracks on the cassette tape. Eight
"Main Data" tracks contain all the PASC data, error correction data and
system information. The ninth, "Auxiliary Data" track holds mainly track and
time information, similar to compact disc, with extra tape markers for easier
operation. Start markers, for example, make track access easy, while reverse
markers are used to initiate auto reverse. The auxiliary data can be scanned
during high-speed search, making operation faster and more straightforward.
All the DCC data on tape is grouped into self-contained tape frames,
separated by InterFrame Gaps (IFGs). To accommodate small deviations in
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the sampling frequency during recording, IFGs can vary slightly in length.
They also help to locate the start points of the tape frames.
Each DCC tape frame contains 12,288 bytes of information (not including
synchronisation). This is composed of: 8,192 bytes of PASC data, 128 bytes
of system information (data for text-mode displays and information such as
copyright and tape type), and 3968 bytes of error detection and correction
The PASC data is spread across the tape frame in a checkerboard pattern
which stops drop- outs (missing signal on the tape due to damage of the
magnetic layer), influencing the quality of the audio performance. Even large
drop-outs will not impair sound quality (see figure 7.6). This can be compared
to interleaving used in CD players, which compensates for any interruptions to
the signal caused, for example, by dirt or grease.
Figure 6 The PASC data is spread across the tape frame in a checkerboard
A Cross Interleaved Reed Solomon Code (CIRC) protects the main data
against random and burst errors. The two layers of CIRC data are spread
across the eight main data tracks. This powerful error correction code allows
for correction of drop-outs even up to 1.45mm in diameter. It can even
compensate for a drop-out bigger than a completely missing data track.
In support of the revolutionary PASC, all the techniques which have made
compact disc synonymous with audio excellence are applied to DCC. All are
closely integrated, and optimised for the tape medium. They are fundamental
to the extreme reliability and quality of this new digital audio system.
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In audio terminology, azimuth is the position and angle of the recording or
playback head in relation to the tape. Azimuth alignment is the position of the
head gap in relation to the position and direction of the tape. Azimuth
difference is a slight discrepancy between the position of the recording head
gap and the position of the playback head gap. Azimuth error refers to
problems in playback that arise because of azimuth differences. If the azimuth
is not adjusted well, the head will not be in the best position to read the
information on the tape and the sound will be negatively affected.
DCC has incorporated
an important advance to
alignment and prevent
azimuth differences and
errors: Azimuth Locking
Pins (ALPs). In
conjunction with the
Fixed Azimuth Tape
mechanism fitted to the
head assembly, the
ALPs ensure not only
tape- to-head contact
(see left inset of figure
7), but also consistent
azimuth alignment (see Figure 7 ALPs and FATG
right inset of figure 7).
The ALPs improve the
wrap-around angle of
the tape against the
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head. This extends the
tape-head contact area
and optimises the
physical conditions for
signal recording and
reading. The exclusion
of gaps in the head
mechanism means less
friction and so less wear
on the tape (which will
therefore last longer).
The tape is also
stiffened in this crucial
tape guidance area, and
this contributes to the
high accuracy of the
In the FATG mechanism, special slots are mounted either side of the head
assembly. The two top edges of the slots are reference surfaces to align the
tape with the head. Meanwhile, the sloping profiles of the lower ports of the
slots gently force the stiffened tape upwards against both reference surfaces.
This simple device eliminates azimuth error.
The ALPs/FATG design requires no complicated mechanisms or close
tolerances. Its very simplicity ensures permanently accurate tape-head
The DCC sound signal is recorded on eight parallel tracks, each 185 µm wide.
The track width required for playback, on the other hand, is only 70 µm wide.
This width factor helps to reduce the sensitivity to azimuth error. An additional
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track carries control and display subcode information.
To achieve these miniature dimensions, the DCC record/playback head
assembly calls on the advanced thin-film head technology already well proven
in multichannel professional recording. In one single head element, three sets
of head elements are combined:
Nine Integrated Recording Heads (IRHs) for digital recording
Nine Magneto-Resistive Heads (MRHs) for digital playback; and
Two Magneto-Resistive Heads for analogue playback.
technology is a major advance in
the thin-film head for digital
playback. MR's high-read
sensitivity allows narrower tracks
to be used for digital coding, so
that overall tape data density is
increased. In addition, MR player
output is independent of tape
Figure 8 Magneto-resistive technology speed. So the problem of varying
is a major advance in the thin-film head output levels with varying tape
for digital playback. speeds, inherent in previous
magnetic head designs, is
The digital heads occupy one half of the head surface, while the analogue
heads occupy the other half. So both digital and analogue tapes can be
handled by the autoreverse head assembly.
In an integrated recording head (one head assembly with recording and
playback functions), the signal current conductor is surrounded by a flux guide
which concentrates the magnetic field into the recording gap in conventional
fashion. The Magneto Resistive Head (MRH)
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There are different types of plastic covers present in the market.They can be
distinguished among themselves on various criteria’s like the shape, colour or
transparency, structure etc..
Cassettes can be classified according to these criteria’s :-
Presence or absence of …………
There are two different sizes of covers available in the market. The
dimensions of the first one are as under :
Length -- 10.55 cms
Breadth -- 6.84 cms
Height -- 1.63 cms
The dimensions of second are as under :
Length -- 11.4 cms
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Breadth -- 7.50 cms
Height -- 2.00 cms
The first kind of cover is basically a system made up of two parts joined
together i.e front and back portions. The front part consists of the front face,
height and a back face which is 39.47 % of the total breadth. It is so
structured that a trapezium shape emerges along its height which is at an
angle of 50 degree at the front portion ( from the left). Its dimensions are as
Length of two parallel sides -- 2.8 cms and 1.78 cms
Height -- 1.63 cms
It is trapezium in shape just to provide the proper area of friction for
interlocking of the two portions. Had the area been more the chances of
breaking of cover increases and had it been less there would be no
interlocking between the two portions. A cut of 2 mm at the back face of the
front part is given at a distance of 1 cm from its end. A similar cut emerges
from the back portion also. This cut is for the ease of separation of two parts
and their free movement. This also provides a little bit of interlocking. These
two cuts are kept apart at a very small distance just to provide free movement.
Theses cuts are not perpendicular to the back face but are at a little slope.
This slope is provided because otherwise a small portion of two cuts would
come over one another and there would have been a difficulty in the closing
the cassette cover.
On the upper and the lower end of the front portion there are two small holes
– one on upper side and other on the lower side. These are at a distance of
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3.9 mm from the left hand side 6.2 mm from the front and back (if one is
holding a cassette while facing its front side). Each end is having a small dent
having a diameter of about 3mm. Its at a distance of 20.5 mm from the left
and 1.5 mm from the front face. The corresponding bulged out portion is
present in the back portion and the two forms the interlocking system. There
are two small vertical joiners, cylindrical in shape having a height of 1mm and
a radius of 2mm on the second part which fits into the two holes of the front
part thus forming a joined system. These cylindrical joiners are placed at the
same place in the back portion as the holes in the front one. These two parts
can rotate at an angle of two hundred ninety eight degrees ( >298 degrees).
There is a small bulging out portion from the back portion which fix into the
small dent in the front portion. There is also a slope present at the right side of
the back portion again for its free movement. Also there are six thin plastic
supports which are used to give a firm grip to the cassette. Each side wall of
the bottom portion contains two supports. The six support are numbered 1 to
6 in the diagram. The supports number 2 and 5 are having a small base. This
is to place the cassette exactly horizontally or in other words to bring the
thinner portion of the audio cassette in level in terms of height with the thicker
The second type of covers are basically a one part system made up of a
single plate with no joining of the front or back portions. Here the cassette is
placed firm in the front door instead of the back wall as observed in the covers
with two parts. While viewing from the inside there are two vertical stands of
height 14mm with a small bulged out area to tightly hold the
cassette(Numbered 3 and 6). At the top portion there are two very small
vertical walls which specifies the area of the cassette. The height of these
walls is 3.5mm. Just behind these walls there are two another walls of a bit
more height (9mm)(Nnmbered 1 and 2) . These are for locking of cassette
cover. The smaller walls in front of these taller walls also grip the walls of the
square from the inside These two walls fits into square holes present on the
other side of the cover(Height 17mm; Area 36mm square) . Also this other
side contains a wall surrounding three of its sides. Also the advantage of this
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kind of cover is that they are more strong and does not breaks in case of a
Cassettes can also be divided on the basis of transparency factor. There are
cassettes which are completely transparent. Secondly there are cassettes
which are having its back portion completely black and the front one
transparent. There is another category of cassettes on the basis of
transparency. It consists of covers which are translucent in appearance.
PREASENCE AND ABSENCE OF ……..
Also cassettes can be divided on the basis of presence or absence of
……….. Also in cassettes where they are present they can be divided into
three categories one having a ……with only two sides, one with three and the
third one with four sides.
Cassette is again cubical in shape. Its dimensions are as under :
Length - 10.00cms
Breadth - 6.35cms
Height - . 85cms
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Some part of the cassette is a little more bulged out as compared to the other
part. It is only this area of length 6.75 cms and breadth 1.2 cms in which the
magnetic tape can be seen and touched. This area is trapezium in shape with
the length of parallel sides 6.35 cms and 6.75 cms and those of the two non
parallel sides is 1.5 cms. The non parallel sides make an angle of 104 degree
with the smaller parallel side. This area is further divided into five parts. On
both the outer edges there are vacant areas of length 1.35 cms and breadth
1cm Then there is a square cut out with dimensions 4mm by 6 mm on both
sides as shown in the figure. In the centre there is another big area of size 1.5
cms by 1cm.There are five holes, four on each corner and the fifth in the
centre from the sides and at a distance of 1 cm from below. These are
basically five slots for screws.
Cassettes basically consists of two parts – the front part (marked as side A)
and the back part (marked as side B), joined together by the above mentioned
5 screws. Also there are four holes each on the front and the back part. Two
of them are completely circular while the other two resembles a bit like
squares. At the upper side there are two square slots at a distance of 6.5mm
from both the ends. In the cassettes manufactured by companies in which
songs are officially loaded and are copywrited the hole is left as such but the
blank cassettes sold on which one store music or signals of his own choice
have this hole covered by a square of the same material. This is because in
the recorder there is a small button. Recording can be done only if the button
is pushed. The blank cassettes have the square placed in the slots which
pushes this button backwards and recording can be done on the cassette. In
the cassettes in which the hole is present the button present in the recorder is
not pushed backward and as a result the recording cannot be done on it. The
figure shows the internal view of the front part. The four sides are marked as
1, 2, 3 and 4. Side 1 is the upper portion of the back part. It contains the two
square parts important for recording in the blank cassettes as described
above. At the toe corners the screws are fixed. The sides 2 and 3 are the
breadths of the cassettes. Side 4 contains the slots for the two screws at the
two corners. The outer and inner diameter of the hole for screws are 4mm and
2mm respectively. This means that firstly there is a cylinder of radius 4mm
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and height s There are also two scoops at the corner right next to the area for
the screws as shown in the figure. These are usually in black or in white color.
Dimensions of one scoop are as under :-
Radius -- 4.0mm
Height -- 5.5mm
The role of these scoops is to give direction to the magnetic tape while the
cassette is being played in the cassette player. There are small spaces left
between two walls at various places of .4mm. These spaces are again to give
direction to the magnetic tape. Actually the magnetic tape passes through
these small areas in the cassette. Beside this there are also four small poles
of height 3.4 mm attached to the front part. The positioning of these poles can
be seen in the diagram(marked as p1, p2, p3 and p4. These poles keep the
two parts a particular distance apart and also stabilizes the cassette. At the
center there are two circular holes, H1 and H2. The diameter of these holes is
1.1cms The distance from the centre of the circle to the side (breadth) is
2.9cms. The distance between the center of the two circles is 4.25cms.
Parts of the audio cassette
Five screws are used in one audio cassette. Four of them are placed at the
four corners of the audio cassette. The fifth one is placed at a distance of
5.1cm from the two breadths and at .95cm from the bottom side……………
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type of screws are used in cassettes. The dimensions of cassettes are as
Height -- 6mm
Smaller Diameter -- .5 mm
Larger Diameter -- 3.2mm
In an audio cassette two scoops are used. The main purpose or role of these
scoops is to provide the direction to the moving magnetic tape in the cassette.
These are placed at the two top corners of the cassette fixed in a rod and
rotating around it. Radius of scoops is 4mm and the height is 5.5mm.
Magnetic tape :
The width of the audio tape is 6.35mm.The sizes generally used are C-30, C-
45, C-60, C-90 and C-120, which specifies 30 to120 minute of playing time.
These are extremely flexible.
In addition to all this there are two black plastic covers which are placed in the
cassette in such a way so as to protect the magnetic tape from the light. This
is jet black in color and thus light in large quantity is not able to penetrate
through it and thus does not affect the magnetic tape or its magnetism. The
structure of this cover can be seen in the figure. Its dimensions are as under :-
Length -- 9.65cms
Breadth -- 4.45cms
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Also there are two circles cut of which are of the same dimension as the……..
and it is placed in the cassette in such away that these circles coincides with
the ……… Also there is a square part of dimensions 2.1cms (Length) and
1.3cms (Breadth) cut out from it.
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Some general terms related to audio cassettes and sound:
The initial point of a sound fro the onset to the point where its amplitude
reaches a maximum.
b) Audio storage
Audio storage refers to techniques and formats used to store audio with the
goal to reproduce the audio later using audio signal processing to something
that resembles the original.
Audio storage techniques:
Analogue recording media:
Phonograph (analogue sound in groove)
o Phonograph cylinder
o gramophone record
Edison Disc Record
Analog magnetic tape
o Reel-to-reel tape
o 4-Track cartridge
o 8-Track cartridge
o PlayTape (Miniature 2-track tapes)
o Compact audio cassette
Digital recording media:
Digital audio tape (DAT)
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Digital compact cassette (DCC)
Compact disc (CD)
Audio file format
o any computer storage, for example digital flash memory cards
Super audio compact disc (SACD)
Frequencies which are within two definite limits, the middle of which is called
the centre frequency.For example, in radio transmission, the standard AM
broadcasting band extends from 550 to 1600 kHz, and the FM band extends
from 87 to 108 mHz. With a qualifying adjective, the term can refer to a certain
range of frequencies roughly described by the adjective, e.g. broad band
noise, narrow band noise.
d) Broad band noise
Broad Band Noise is a type of noise which has its energy distributed over a
large section of the audible range. Its also called Wide band noise, and the
opposite of Narrow Based Noise.
The output of most ventilation ducts is an example of steady broad band
noise, and a jet engine flyover could be classed as TRANSIENT broad band
noise. Most motors, including those in household appliances, produce a great
deal of such noise, often with much of its energy in the higher frequency
region where the human ear is the most sensitive (1 to 4 kHz). This aspect of
the sound is not given special account in decibel measurements, and thus
such measurement systems as the perceived noise level, noise rating and
noise criterion, and their derivatives and extensions have been devised.
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e) Bulk Eraser
A device for the quick removal of the recorded signal on an entire reel of
magnetic tape. The tape is exposed to a strong alternating magnetic field
which removes the recorded signal. The device is also called a degausser.
f) Centre Frequency
The frequency in the middle of a band of frequencies, by which the band is
identified together with the bandwidth.
For instance, in the standard octave band from 177 to 354 Hz, the centre
frequency is 250 Hz.
In electronic sound synthesis, it refers to the frequency of the unmodulated
carrier signal or the middle of the frequency range to which equalization is
A discrete path or frequency band permitting the transmission of messages or
signals. The width of the channel is usually restricted to accommodate just the
types of signals employed in the messages, e.g. the telephone is restricted to
the frequency band just necessary for the accurate comprehension of speech.
The determination of channel capacity for information is studied in
In Tape recording, the number of channels or tracks refers to the number of
discrete signals which may be recorded at one time, as in monophonic,
stereophonic, quadraphonic and other multi-track formats.
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The process whereby the amplitude of oscillation of a vibrating system
diminishes with time due to a loss in energy. In terms of the envelope of a
sound, it refers to the final part of the sound, including effects of reverberation.
To demagnetize; for example, demagnetizing a tape head, in order to remove
A momentary decrease in loudness noticed during magnetic tape playback as
the result of tape imperfections in the emulsion which prevent close contact
between tape head and tape being maintained during recording.
The oxide coating on magnetic tape, composed of microscopic magnetizable
particles suspended on a plastic film base or backing, such as acetate,
polyester or mylar. During recording, the particles are re-aligned in
correspondence with the input signal, and later during playback, these
particles (also called domains) induce a similar current which reproduces the
original signal. Tape without emulsion is called leader tape.
The structure of magnetic recording tape.
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Realignment of magnetized particles during the recording process.
Audio Signal Processing
Audio signal processing, sometimes referred to as audio processing, is the
processing of a representation of auditory signals, or sound. The
representation can be digital or analog. An analog representation is usually
electrical; a voltage level represents the air pressure waveform of the sound.
Similarly, a digital representation expresses the pressure wave-form as a
sequence of symbols, usually binary numbers.
The focus in audio signal processing is most typically an analysis of which
parts of the signal are audible. For example, a signal can be modified for
different purposes such that the modification is controlled in the auditory
domain. Which parts of the signal are heard and which are not, is not decided
merely by physiology of the human hearing system, but very much by
psychological properties. These properties are analysed within the field of
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Processing methods and application areas include storage, level
compression, data compression, transmission, enhancement (e.g.,
equalization, filtering, noise cancellation, echo or reverb removal or addition,
etc.), source separation, sound effects and computer music.
Baking" magnetic tape to overcome the "sticky-shed"
What's It All About?
By now, every audio-professional has encountered the "sticky recording tape"
problem, and has heard that something referred to as "baking" will fix the
problem. The truth of the matter is "yes" and "no". Yes, the problem can be
temporarily corrected by the "baking" process, but no, the cure is not
The problem goes back to the 1970's when most tape manufacturers made an
ill-advised decision to change the formulation of the "binder" used to glue the
magnetic tape particles to the plastic base material. Unknowingly, the new
formulation attracted moisture, and eventually enough accumulated to make
the tape go "sticky".
The purpose of "baking", is to drive out all the moisture that the tape binder
has accumulated, which is what caused it to go sticky in the first place. This
will give a few weeks to a few months of "normal" tape functioning... enough
time to transfer the affected recordings to a stable medium before the problem
reappears when more moisture is absorbed.
Essentially, the process is this... put the tape in an electric oven with an
accurate temperature control set to 130 degrees Fahrenheit, for about 4 - 6
hours. Do not use a gas oven... gas produces water vapor when it burns, and
that is what you are trying to drive out of the tape. Ensure the temperature is
accurate with a lab quality thermometer or use a "known to be accurate" oven.
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A slight variation (plus or minus 5 - 10 degrees Fahrenheit) above and below
this temperature is acceptable.
Never attempt to bake tape without an accurate thermometer!
Place the tape on the reels in the oven and bring the oven slowly up to
temperature. Allow it to cool back to room temperature before removing the
It is the moisture absorption that caused the problem, and to correct it, you
have to drive off the moisture that accumulated. The oven technique is the
fastest and probably the easiest way to do this. Handling is pretty much
normal after the baking, and will probably last for some time until the tape
accumulates enough moisture to go sticky again, whereupon re-baking will
temporarily fix it again. It is suggested that you do a good transfer the first
time, and file the bad master away somewhere, just in case you ever need it
again, perhaps in a sealed plastic bag with some desiccant material inside,
like a bag of silica-gel, to keep it dry.
Check out the Issue 12 1995 issue of EQ. There are notes on this subject in
the EQ & A column from an Ampex engineer and also from BASF Magnetics.
More technical details...
Audio tape manufactured in the mid-to-late 1970's is starting to come out of
storage now, for remixing and re-issue, and engineers are finding that it won't
play. The surface of the tape has become gummy and it sticks to the heads
and fixed guides of the tape transport, squealing, jerking, and, in extreme
cases, slowing down or stopping the tape transport. This problem has
cropped up on all brands of tape, but is nearly always fixable, at least
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Tapes can exhibit two different problems as a result of long term storage;
binder breakdown and lubricant breakdown. Lubricant breakdown, which is
fairly rare, leaves a white residue when the tape is run over the heads. Binder
breakdown, the more common failure mode, leaves a dark, gummy residue,
and is fixable by gentle heating ("baking") of the tape. Fixing lubricant
breakdown requires careful cleaning of the tape and possibly applying fresh
lubricant. Baking will not solve the lubricant breakdown problem and may
make it worse. Make sure you know which problem you have before you put a
tape in the oven.
Here's where the stickiness comes from. The binder is the chemical
compound that holds the oxide particles together and sticks them to the tape
backing. Under humid conditions (which means anything but controlled low-
humidity storage), the polyurethane used in the binder has a tendency to
absorb water. The water reacts with the urethane molecules, causing them to
migrate to the surface of the tape where they gum up the tape path during
Short strings of urethane molecules are particularly prone to water absorption,
while long strings make the coating mixture too viscous to produce good tape.
Middle-length strings are the best, but the tape manufacturers didn't know this
at the time, and didn't always know what they were getting.
In the case of Ampex tape, tapes most likely at risk are 406 and 456
manufactured from approximately 1975 through 1984. During those years,
Ampex tested the goop they got from their binder suppliers simply by
measuring viscosity. Unfortunately, the long and short strings average out,
viscosity-wise, to a viscosity about the same as the ideal medium strings, so
some tape was inevitably manufactured with an overly great proportion of
short urethane strings in the binder. In the worst cases, as little as 3 days
exposure to 70% relative humidity can cause a tape to become gummy, but
typically, it takes 2 to 15 years under normal, people- friendly ambient
conditions. In 1984, Ampex started doing it's incoming inspection with a high
pressure gas chromatograph (that's when it was invented), and was able to
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more accurately determine the molecular makeup of it's binder, and control
production much more carefully.
The good news is that the "sticky shed syndrome" resulting from water
absorption by the short urethane molecule chains is almost always fixable.
The process for repair is commonly know as "baking a tape". The fix lasts
about a month under normal storage conditions, and Ampex claims that a
tape can be re-baked any number of times without ill effects. Best advice,
though, is to make a copy of the tape on first playing, and work with the copy.
To bake a tape, you want to expose it to even heat, ideally at 130 degrees
Fahrenheit, with a variation of less than plus or minus 10 degrees. Too cool
and the process is ineffective, too hot and you're starting to risk increasing
There are several kinds of ovens you can use. One thing you DON'T want to
do is stick it in your kitchen oven and turn the heat on "low" unless you have
carefully tested the characteristics of your oven. Most oven thermostats don't
go low enough, or don't provide good enough temperature control. Whatever
you choose, DON'T use a gas oven... a gas flame generates quite a bit of
water vapor, which is exactly what you're trying to get rid of.
It's important that the tape be packed smoothly before baking. Chances are it
will be if it's been cared for as a master tape should, but if it needs to be re-
packed, this should be done by winding the tape at play speed on to another
reel using a tape deck on which the heads can be removed, and with the tape
threaded so that it doesn't pass over any fixed (non-rotating) guides.
Baking time ranges from about 4 hours for 1/4" tape to 8 hours for 2" tape. It's
not critical. You can't over-bake unless you leave it for a day or so and if you
under-bake and the tape is still gummy, you can bake it more. After you shut
off the heat, leave the tape to cool down to room temperature before running it
through the deck again.
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If you want a more elegant solution, check your local appliance shop for a
Faberware (or equivalent) convection oven, but make sure it's large enough to
accommodate the size tape reels you use. These run about $150 and might
be a worth while investment if you have a large amount of tape to bake.
Ensure the temperature control is accurate by using a "lab" type thermometer
to test the oven's performance BEFORE using it on valuable tapes.
DO NOT ATTEMPT TO USE A MICROWAVE OVEN... they are totally
inappropriate for the job, and may be dangerous if used with metal reels.
Lately, I've been doing tapes in my pilotless kitchen oven, by replacing the 25
watt appliance lamp inside with a standard 100 watt light bulb, and putting in a
muffin fan salvaged from a dead PC power supply to circulate the air. That
gives me a nice stable 130 degrees, but it took some experimenting with the
fan speed and placement. Without the fan, it never got beyond about 110
degrees, and I found that a 150 watt bulb (my first test) wouldn't allow me to
get below 140 degrees. The friend who told me about this approach says he
does it in his kitchen oven with the standard bulb that was in there when he
bought the house. Go figure.
The technical jargon about the molecules comes from an article by Philip De
Lancie in the May 1990 issue of Mix Magazine, where he quoted sources from
Ampex. I'm no molecular chemist, just giving credit where it's due (and
relieving myself of the responsibility for errors).
83 | P a g e
This is the standard workhouse for home entertainment systems.
Internationally, this is produced subject to strict guidelines laid down by the
International Electro-technical committee which recognizes four categories of
audio tapes :
Type 1 tapes which requires a playback equalization response of 120
microseconds and a normal bias.
Type 2 tapes requires a playback equalization response of 70
microseconds and a high recording bias.
Type 3 tapes requiring a 70 microsecond playback equalization and a
Type 4 metal tape requiring 70 microsecond playback equalization
and a high recording bias.
Bias is an inaudible signal used to correct the discrepancy between the
magnetic pattern recorded on the tape and the magnetic field
generated by the recording hard of the cassette deck.
Equalization is a technique used to compensate for the fact that no
cassette deck reproduces signals with a flat frequency response.
All the four of audio tapes are available in 60 and 90 minutes lengths.
The basic difference in technology lioes in the formulation of the
coating slurry which is build around an oxide.
84 | P a g e
The term “erasing” is used instead of obliterating only because it is more
easily understood and less clumsy. Erasure, however, improperly connotes
shaving, scraping, or removing of material. Obliterating (which is the term
always used in German scientific literature) may also imply the defacing or
destroying of marks. The actual process more closely resembles the
obliteration of sand writing by surface smoothing since material is not actually
The magnetic erasing process (or more properly the electromagnetic erasing
process) is in reality a demagnetizing procedure which completely removes
previously recorded signals without affecting the magnetic tape in any other
way whatsoever. This makes it possible to efficiently use the same tape over
and over again, a unique advantage enjoyed by magnetic recording, which
cannot be claimed for any other recording process.
It has been known for a long time when a magnetizable substance has been
magnetized and is subsequently subjected to a progressively diminishing
alternating field, the magnetized medium will eventually arrive at a neutral
state. This is accomplished through a series of gradually decreasing
hysteresis loops which finally become infinitesimally small, so that the normal
induction curve ultimately terminates at a point where H equals zero and B
equals zero, which is the neutral point as defined for a demagnetized
ferromagnetic specimen. Figure 9-1 indicates the change in the magnetic
state which accompanies a gradually decreasing magnetic field produced by
85 | P a g e
ALTERNATING FIELD ERASURE
Early experimenters in magneto-magnetics experienced a considerable
amount of difficulty in attaining the absolute neutral state because of the
problems encountered in reducing the final hysteresis to absolute zero. Their
difficulties were caused more by the methods employed than the principles
involved. When complete demagnetization of a stationary medium is
attempted, the last stages of the demagnetization process become critical
since the magnetizing current must be first reduced to zero before the circuit
is opened. Any sudden break during demagnetization of the demagnetizing
current will prevent the attainment of absolute zero magnetic induction.
In normal process of magnetic recording, however, this difficulty is
automatically eliminated. To accomplish complete demagnetization, an
erasing head is employed which is usually similar in general construction and
appearance to the record produce head. The basic difference in construction,
however, lies in the length of the gap. In order to produce a diffuse field, the
erase gap length may be as much as 200 times as long as the gap in the
similar playback head. Gap length usually used is approximately 20 mils.
Another difference lies in the relative unimportance of the alignment of the
gap edges. Precise alignment techniques are not required other than to insure
reasonable uniformity in inductance from head to head and to provide a
sufficiently intense external field. By feeding a relatively high voltage to the
erase head so as to produce an external field at the point of tape contact
ranging between three and five times the coercivity of the tape sufficient stray
flux is produced near the lagging and leading edges of the gap to gradually
subject the tape to an increasing and then a constantly decreasing field.
With an ultrasonic erase frequency of 50,000 cps and a tape speed of 7 ips,
each magnetic particle is subjected to well over 150 reversing magnetic fields
as it travels the length of the gap (0.025 of an inch) in 3.33 milliseconds. This
number of reversals is more than adequate to affect complete erasure.
To insure thorough erasure it is, of course, important to design the circuit and
associated components so that the peak erasing field exceeds the maximum
instantaneous peak of any signal on the tape which is another way of saying
that the initial demagnetizing current should he sufficient to carry the induction
86 | P a g e
beyond the knee of the B-H curve and the minimum current should not be
greater than the smallest magnetizing recording current used.
In a properly designed system it is relatively simple to attain complete and
perfect erasure. In fact, many professional and semi-professional machines
actually erase fully modulated tapes to a quieter state than that of their virgin
The Effectiveness of Erasure
If we assume that magnetic tape is manufactured under idealized conditions
(these idealized conditions are not always prevalent particularly when some of
the rollers, slitters, or other elements of the coating, slitting and winding
machines become magnetized), the magnetic domains within the medium
assume random positions and fields. As long as the statistical average of
these fields for any given length of the medium is equal to zero, the medium
may be considered unmagnetized. This definition which applies perfectly to
usual forms of bar magnets fails significantly when applied to magnetic
recording. If the playback head has a resolution of 0.1 mil it will, in effect,
successively scan very short sections of virgin tape. Because these lengths
are so minute, it is highly improbable that the statistical average of the
magnetic domains in successive minute lengths will consistently equal zero or
be entirely neutral. As a result the head actually scans varying magnetic
gradients which have assumed random positions merely as a matter of
chance. These varying magnetic gradients are detected by the playback head
and heard as tape noise. When the tape is properly demagnetized, however,
the statistical average of the magnetic domains within the extremely short
distances scanned by the head are consistently equal to zero, so that the
head itself continually scans successive media having a zero magnetic
gradient and will, therefore, not detect any random noises.
Although the basic principles of perfect erasure are easy to understand they
are not quite so simple to apply in practice. Though the design of the erase
87 | P a g e
head follows the general idea of the recording playback head, there are a
number of critical factors involved in its construction.
In most recording equipment the same high frequency is used for biasing and
erasing with the result that core losses are significant. The core material of the
head is subjected to both hysteresis and eddy current losses which inevitably
result in heat. If the heat dissipation of the erase head is not adequate, the
plastic tape or the plastic binder in the coating of paper base tape may either
soften or tend to stick to the head. For this reason, improperly designed
systems cannot have their tape travel stopped for any appreciable length of
time with the tape contacting the head while the circuit is set up for erasing.
For perfect erasure, the recording head itself must not become magnetically
polarized. Furthermore, the waveform of the erasing voltage must be
absolutely symmetrical. An unsymmetrical waveform or a polarized head will
leave residual magnetism on the tape which, in turn, will highlight any
irregularities in the magnetic medium and produce significant noise.
It is of passing interest to note that earlier systems invariably utilized d. c.
erase which first completely saturated the medium and then brought the
residual induction back to a linear portion of its transduction curve. Direct
current erase, however, because of its characteristic residual noise it has
been virtually abandoned in all but low-price or special equipment.
In addition to the conventional erase heads of the a. c. or d. c. type other
forms of erasure are also available to meet specialized needs. Included in this
88 | P a g e
group are bulk erasers which erase complete reels of tape without the
necessity of unwinding or rewinding. Permanent magnet erasers are
representative of still another class which do not draw any electrical energy
from the ultrasonic oscillator or recording amplifier.
Occasional faults in the erasing components of some magnetic recorders and
the rapid development of specialized tapes have justified the production of
bulk erasers which utilize 60-cycle current for complete erasure of a full reel of
tape without rewinding. With this quick method of erasing, it is easier to attain
complete erasure without conforming to the stringent requirements necessary
for perfect ultrasonic erasure.
PERMANENT MAGNET ERASURE
Although ultrasonic erasure closely approaches the ideal technique, there are
at times attractive reasons for utilizing a permanent magnet for erasure. Such
reasons may include economy, dependability permanence, and extreme
The ease with which permanent magnet (p m) erasure can be applied does
not offset the difficulty of avoiding residual magnetism on the tape after signal
erasure. Since contact with either pole of a magnet will leave the tape fully
magnetized, this type of erase will result in relatively high noise levels and will
introduce serious even order harmonic distortion in subsequently recorded
To minimize this effect, more than one permanent magnet pole way be used
SO that the tape is left in a nearly demagnetized condition. A very large
number of poles of successively opposite polarity and gradually decreasing
fields are of course, equivalent to an a. c. erase, but a practical design may
involve the use of a small number of poles as an approximation.
One system in common use employs two magnets arranged to give
essentially a three pulse erasure. (See Figure 9-3.) The tape is subjected to
opposite field maxima at points A, B, and C. At point A the magnet contacts
89 | P a g e
the tape and subjects it to a saturating field which erases previous recordings.
The function of the fields at B and C is to leave the tape essentially
demagnetized. This is accomplished by adjusting the distance between the
tape and the poles at B and C to the correct separation so as to give the best
ultimate values of neutralizing fields.
In battery-operated recorders where conservation of space, weight, and
batteries are of prime consideration, some form of p-m erase may be justified.
Permanent magnet erasure may be included in the form of a ring magnet
combined with a rotatable tape guide as illustrated in Figure 9-4. Permanent
magnet erase systems invariably add from 2 to 6 db of noise over and above
that attainable with ultrasonic erasure, and should therefore be cautiously
used when wide dynamicranges are required.
Some of the processes involved in magnetic recording are characterized by a
number of peculiarities which at first glance do not appear to comply with
classical theories of magnetism. The tremendous impetus that magnetic
recording received during the last fifteen years has brought many serious-
minded investigators into the field who have observed and studied
phenomena previously either lightly touched upon, or completely ignored in
classical magnetic studies.
It has always been known that a magnetic gradient exists in every bar magnet
regardless of its length. It has also been assumed that the gradient displayed
a smooth or continuous function. In an ordinary 2- or 3-inch bar magnet it
makes very little difference whether the magnetic intensity diminishes in a
precise and smooth manner from either pole to its center. In fact,
measurements of deviation of this smooth function in most applications were
relatively unimportant. In magnetic recording, however, this simple and
90 | P a g e
unobtrusive quality of a bar magnet is of prime importance. The very nature of
playing back a recorded signal involves the minute scanning of a magnetic
medium for deviations in magnetism An idea of the minuteness of this
scanning process may be gathered from the effective length of the
playback gap which, for most slow speed machines is approximately 1/10,000
of art inch or less. When such a minute gap scans a length of recorded
material, it is in essence “looking for” magnetic deviations within extremely
short sections of tape (0.00025 of an inch). Furthermore, when a signal is
recorded, the scanning or playback device actually detects a rate of change of
magnetic induction from one infinitesimal area to the next. Obviously, any
mechanical, chemical, or magnetic function winch interferes with this scanning
or play back process will interfere with magnetic recording.
NOISE IN MAGNETIC RECORDING
Before magnetics was used for recording, the term “magnetic modulation
noise” was unheard of. Today, it offers an exciting challenge to the
magnetician. Although noise exists in every form of re- cording, it has
received a great deal of attention in tape recording because, at the present
stage of the art, it is a limiting factor in the extension of dynamic range.
Noise in magnetic recording has already been arbitrarily classified in a
number of ways. Actually, the fundamental classifications are magnetic,
mechanical, and electrical.
Magnetic noises may be broadly defined as all noise contributed by the
magnetic properties of the recording medium. It includes modulation noise
and all other tape noise caused by irregularities in the medium.
Mechanical noises may be defined as all extraneous noise introduced into
recording or playback systems because of mechanical deficiencies. These
include flutter and amplitude variations produced by poor head-to-tape
Electrical noises in any recording system are the result of extraneous sources
of sound introduced by the electrical components of a system. They are
usually caused by intermodulation, ambient magnetic fields, tube and other
91 | P a g e
Although these three types can be broadly separated by definitions, they are
usually so interrelated that it is sometimes exceedingly difficult to sharply
isolate one from the other.
Nearly all, if not all, of the magnetic noise in magnetic recording systems may
be traced back directly to the recording medium. As all forms of magnetic
noise stem from one basic deficiency, magnetic heterogeneity, it is desirable
to review magnetic noise-producing processes. Modulation Noise Analogy
For an elementary explanation, it might be helpful to use a “smooth” piece of
fur for purposes of analogic comparison. When such a piece of fur is stroked
in the direction of its nap it will feel smooth. If we now electro statically charge
it so that all of its hairs are upright, a marked irregularity will be noticed in its
‘l’his roughness is caused by uneven hair lengths. If these hairs were all cut to
an equal length they would present a relatively smoother appearance.
Nevertheless, some of the hairs will assume upright positions and others may
he deviated from the perpendicular depending upon the thickness of the
individual hair. (It will be tacitly assumed that the thinner hairs will more
readily respond to an electrostatic
charge than the thicker ones.)
If we had an idealized piece of fur with equal hair lengths and equal hair
diameters, the smoothness of its upper surface when subjected to an
electrostatic charge would be materially improved.
If we remember that a coated magnetic tape is composed of particles of
magnetizable material and that each of these particles not only varies in
size, but is different in shape. and may not be uniformly dispersed within its
binding medium amid may, furthermore, not be uniformly coated upon a
perfectly smooth base, some of the factors which will affect its
magnetization become readily apparent. However if we could imagine an ideal
magnetic fluid which is completely homogeneous it would be entirely devoid of
92 | P a g e
Instead of electro statically charging a fur piece we might attempt to uniformly
magnetize the recording medium. This can be accomplished by passing the
tape over the head of a permanent magnet. The magnetic strength should be
such that the residual induction in the tape roughly corresponds to time rms
value of the normal recording signal. With this treatment the magnetic layer
will exhibit a degree of magnetic orientation dependent upon all of the
factors which contribute to magnetic noise. When such a magnetized
tape is subsequently played back (through a wide band system) the
measured noise will be an excellent indication of the magnetic uniformity of
the tape. It will be note (1 that when time effect of the permanent magnet is
decreased by interposing some significant space between the magnet and the
tape, the noise will be relatively reduced. Figure10-1 indicates the relative
degree of noise produced as a function of intensity of magnetization.
Inasmuch as any modulating signal is nothing more or less than an
instantaneously varying degree of polarized magnetization, it follows that any
recording medium which is characterized by magnetic noise will in turn
produce noise as ‘a function of the degree of its instantaneous magnetization.
Therefore, when a sine wave signal is mpressed upon a non-ideal magnetic
medium, modulation noise will be apparent in proportion to the instantaneous
value of the modulating signal. This condition is illustrated in Figure 10-2. It
may be measured by first recording a fixed frequency at or near the normal
recording level and then subsequently filtering this frequency from the
playback. All residual noise over and above that which exists when completely
erased tape is passed through the same recorder may be attributed to
magnetic noise, or specifically in this case, to modulation noise.
Magnetic noise will also make itself apparent in any non-ideal magnetic
medium when it is subjected to any form of polarized voltages For example, if
an ultrasonic bias is employed with a pronounced even-order harmonic the
residual or unbalanced remanent magnetization will make itself known by
Magnetic modulations and noise can be impressed by other than electrical
means; it can be done magnetically. For example, if the recording or erase
heads become magnetized they in turn will subject a magnetic medium to a
constant or intermittent magnetic modulation which will display deficiencies in
93 | P a g e
the magnetic coating by producing magnetic noise; Other magnetized
elements which contact the tape may likewise magnetize the medium. Rollers,
guide posts, tensioning devices cut off switch elements etc., must not become
magnetized if the recording system is to be entirely free of magnetic noise.
Magnetic noise, while being objectionable, in itself contributes further
undesirable characteristics to the recording system by producing
intermodulation products between the random noise frequences and the
recording signal frequencies. These intermodulation products may produce an
indescribable form of distortion, sometimes characterized by a fuzziness or
roughness, depending a. greatdeal upon the nature of the program material.
HEAD-TO-TAPE CONTACT NOISE
The most critical point in a recording and playback system is the area at which
the recording or playback head contacts the tape. This area is known as the
point of translation, because it represents the exact position at which
conversion takes place from magnetic to electrical fields or vice-versa. An
idealized point of translation should provide a constant area of contact
between the tape and the gap of the head, free of all other extraneous
movements, excepting, of course, a continuously smooth longitudinal motion.
If for any reason the head vibrates transversely in relation to the tape, ii will in
effect be making and breaking physical contact with the tape. While contact in
the electrical sense is relatively unimportant (excepting for possible
electrostatic effects) actual physical contact is of vital importance because of
the extremely short recorded wavelengths impressed upon tape traveling at
slow speeds. A 7,500 cps tone recorded upon tape traveling at 7 ips produces
a recorded wavelength of 1/1,000 of an inch: The maximum magnetic gradient
that the head should scan is approximately one-fourth of this length,
This minute dimension of 0.00025 of an inch should be at least twenty times
greater than the varying distance between the head and the tape. This means
that the head-to-tape distance should not exceed 0.0000125 of an inch. If this
distance remained constant a fixed loss. (as a function of frequency) would be
evident. Random variations of this distance produce random variations in the
amplitude of the playback signal. The net result is a signal which is
94 | P a g e
indistinguishable from one of an equivalent frequency with injected noise
The loss in level caused by separation between the playback head and the
tape depends upon a separation factor Sf which is functionally related to the
recorded wavelength, or to the signal frequency and tape speed in
accordance with the following expressions:
S = separation factor
$ = recorded wavelength
^ = space between head and tape in inches
F = frequency of recorded signal
v = tape speed in ips
The actual separation loss in db is a logarithmic function of the separation
factor derived from the following formula:
SL 20 log 2rS
S= 54.6 Sf db
SL = separation loss in db
Sf = separation factor
The loss in db at any frequency, tape speed or wavelength can be estimated
(after the separation factor is determined) from the curve of Figure 10-3. It
‘can be seen that minute variations in separation distances are far more
95 | P a g e
deleterious at the shorter wavelength (higher frequencies) than at the longer
wavelengths. Recorders operating at higher tape speeds of 15 or 30 ips
exhibit less effect for a given separation between tape and head. In fact, the
higher speed machines rarely utilize any pressure pads for tensioning the
tape against the head because the highest recorded frequency has a
relatively long wavelength.
CAUSES OF HEAD-TO-TAPE CONTACT VARIATION.
Separation between tape and head may be brought about by a number of
mechanical deficiencies. If the compliance of the tape is low, that is, if t is too
stiff, it may or may not always follow the contour of the recording or playback
head. If the tape becomes excessively wrinkled, cupped, curled, or otherwise
deformed because of uneven moisture absorption or through improper
winding tensions, it may not always be in intimate contact with the head.
CAUSES OF MAGNETO-MECHANICAL NOISE.
(Mechanical noises which are audible outside the system are not among the
deficiencies being considered.) There are many causes which may contribute
to the minute instantaneous discontinuity of movement at the point of
translation so that even though tape appears to be smoothly sliding over the
contour of the magnetic head, it may be far from an ideal continuous flow.
The nature of the tape base itself, being a plastic, stretchable medium, makes
it sensitive to variations in longitudinal stresses.
Therefore, instantaneous variations of tension within the tape, particularly at
the point of translation, must be kept at a minimum to avoid conversions of
these tension variations into magnetic noise.
Variation in the coefficient of friction between tape and head will produce a
longitudinal vibration in the tape (sometimes called “via lining” because it
corresponds to the longitudinal stresses set up in a violin bow when playing).
Pressure pads, increasing the ambient coefficient of friction, will tend to
magnify this effect. It is for this reason that the addition of a pressure pad.
Though it raises the signal level picked off the tape in some recorders, also
96 | P a g e
raises background noise. An effective increase in dynamic range is not always
attained, unless increased longitudinal vibration is avoided. Modern highly
polished and lubricated tapes overcome most tendencies towards longitudinal
Tape chattering caused by uneven movement past guide posts may result in
variations of the distance between tape and head. When these variations are
random, as they usually are, the amplitude changes exhibit themselves as
random noise, the predominant frequencies of which become a function of the
rate of vibration of either the tape or some of the tape guiding and driving
Sometimes mechanical noises are introduced into a magnetic recording
system by the actual change in arrangement of the magnetic domains within
the tape by the tape handling mechanism. If an extraordinary amount of pinch
effect is required, in order to provide intimate contact between the tape and
the capstan to assure a constant speed of tape travel, this extreme pressure
may minutely reallocate magnetic particles within the medium resulting in a
displacement of an otherwise smooth magnetic gradient. When this condition
exists it will be found that noise may increase with increased number of plays.
MULTIPLE SCANNING NOISE
Other apparent sources of noises in magnetic recording which may be traced
to malfunctioning equipment include incomplete erasure, and lateral head
misalignment. In a multi track system utilizing a movable head, it is imperative
that the head he laterally displaced in accordance with the original recorded
track. If, for any reason, the head simultaneously scans two tracks,
extraneous signals will be heard as background noise.
It is sometimes difficult to differentiate between incomplete era- sure and
multiple track scanning. The use of a bulk eraser will eliminate the former
possibility while checking for the latter.
97 | P a g e
INVISIBILITY OF MAGNETIC RECORDING
Occasionally specialized technicians raise an incidental objection to the whole
art of magnetic tape recording because of the invisibility of the recorded track.
In motion picture techniques, where a great deal of re-recording and accurate
synchronization between sight and sound are an absolute necessity. The
invisibility of magnetic recording is obviously a handicap.
Magnetic recordings can be made visible by employing a special refinement in
the usual method of plotting magnetic fields by sprinkling iron powder over the
area to be investigated. Because of the minute dimensions normally
encountered in magnetic recording, the usual form of iron powder would be
far too coarse to display any usable visible pattern when randomly sprinkled
upon recorded tape.
In order to obtain a high degree of resolution and good visibility against the
black or red background of tape, carbonyl iron should be employed. For an
even dispersion of the glossy iron particles over the rape it should be
suspended in a liquid which will evaporate without damaging the backing or
the binder of the tape. Any hydrocarbon. such as heptane of high volatility is
satisfactory. The iron particles employed should he approximately 2 microns
or less in diameter. The recorded tape may be passed through the agitated
solution and then placed on a Hat surface to dry
Where extreme definitions of very small recorded wavelengths are required
finer iron particles may he suspended in a light fixed oil So that they will very
gradually settle Into a visible magnetic pattern which corresponds to the
magnetization of the tape. Figure 10-4 is a photomicrograph of a dual-track
recording made visible by passing it through a suspension of carbonyl iron in
heptanes. UNIQUE MAGNETIC TAPE PHENOMENA
DELETERIOUS MAGNETIC MEMORY
Many peculiar characteristics have been attributed to magnetic recordings
which have not been subsequently substantiated. For example, one
investigator reported “tape return memory.” It was shown (because of some
still unexplainable aging processes of magnetic materials) that a recorded
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tape stored at a relatively high temperature for a long period of time could first
be completely erased and subsequently treated to restore the erased signal.
After testing the tape for complete loss of signal by playback, it was subjected
only to the ultrasonic biasing field of the record head by putting the tape
through the usual recording process silently (without actually recording a new
Playback then produced the original signal which was explained as having
been “memorized” by the magnetic domains in the tape. This interesting
phenomenon was very carefully investigated under controlled conditions and
was found to be a peculiar combination of inadequate erasure plus the effects
of a specialized biasing field. During the initial erasing process only a portion
of the magnetic layer was erased. Throughout playback this erased layer
acted as a magnetic shield between the unerased lower level of the magnetic
medium and the playback head. Under conditions of subsequent recording,
with the biasing field only, a form of incomplete erasure again took place
whereby the upper layer could not be magnetically reduced to a neutral stage
because of the influence of the lower layer.
As a result, the upper layer acquired, to a small degree, a portion of the
magnetization of the lower layer.*
Characteristics of “tape return memory” have not been found by the writer in
samples which had been recorded at a high level and stored for a period of
eight years at temperatures ranging between 70 and 100 degrees F.
Subsequent thorough erasure in a standard recorder completely eliminated
every trace of original signal and under no subsequent treatment could any
characteristics of this queer tape memory be detected. In this respect,
classical magnetic theory specifically indicates that once a magnetizable
medium has been magnetized, its past history is completely lost. The same
holds true under conditions of full demagnetization This process has
subsequently been the basis of an attempt for producing multiple recordings
by providing a master which contacts blank tape under the influence of a
weak biasing field. Because of serious frequency discrimination which
occurred, this form of “contact” duplication (without re-recording) does not
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SINGLE-, DUAL AND MULTITRACK
As magnetic wire was the original medium utilized in the early development
and application of magnetic recording, the concept of more than one
recording track on a hair-like wire was untenable. With the subsequent advent
of ¼ inch and wider metal, paper, and plastic tapes, the idea of multiple track
not only seemed reasonable but easily attainable.
It should be remembered that the term single-track is descriptive only to the
extent that it specifically indicates that one track is re-corded on the tape.
There is no connotation as to the width of this track though it is tacitly
assumed that the track is recorded in the center of the tape. When only one
track is recorded on a dual-track recorder the recording is described as single-
track though the track may be laterally displaced and narrower than usual
Although tape has been standardized at a width of an inch it would be
erroneous to assume that the actual recording track covers the full width of
the tape. Usual single-track recording widths vary from 0.118 t 0.245 of at inch
depending upon design objectives,
To secure complete erasure of magnetic recordings, the erase track is always
made wider than the record track. A typical set of relative record and erase
track widths is indicated in Table 1
A minimum of a 6 mil erase overlap on both edges of the track is necessary to
compensate for lateral tape weave and production tolerances in lateral
misalignments between he record and erase heads. If both the record and
erase tracks were precisely alike in width, misalignment for any reasons
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whatsoever would prevent complete erasure of the original recording
Increasing the width of the erase track also insures erasure of fringe
magnetization, i.e., the leakage flux which extends beyond the expected
sharp edge of the recorded track.
VARIATION OF TRACK WIDTHS
For maximum signal-to-noise ratio, recorded tracks should be as wide as
possible. Practical limitations, however, dictate the use of track widths far less
than the theoretical maximum.
Residual Noise Level. As the residual noise level on tape is a function of the
magnetic heterogeneity of the tape it would appear that the more magnetic
domains instantaneously scanned by the playback head, the more likely
instantaneous variations between longitudinally adjacent sections would be
negligible—resulting therefore in decreased residual noise. To put it another
way, supposing a single string of magnetic domains were arranged
longitudinally on a tape. If a playback head could be designed to scan and
respond to this microscopic track, the magnetic orientation of each domain
would produce a random (noise) response. If a thousand such tracks were
now laid laterally side by side and the scanning width of the playback head
increased a thousand fold then a thousand randomly disposed domains would
be scanned at once. The statistical probability of an average cancellation of all
scanned domains from instant to instant is far greater than with a single
domain chain. The increased average similarity of adjacent sections would
result in lowered noise.
SIGNAL LEVEL VERSUS TRACK WIDTH
All other factors remaining constant, the amount of energy induced into the
playback head is related to the width of the scanned track. Wider tracks
produce greater signal levels. As these power level ratios are comparable to
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relative acoustic levels, doubling the track width doubles the power and raises
the level by 3 db In effect relative power levels of varying width tracks are
expressed as follows:
db = 10log (Wa/Wb)
where db = decibel level change
Wa width of track A
Wb width of track B
As a matter of practical application it is interesting to compare the relative
calculated differences in levels for the various track widths presently used.
These are indicated in the sixth column of Table 1. It is to be noted that actual
levels (shown in last column) obtained from commercial he bear little
significant relationship to calculated values because many design factors
other than track width enter into the relative efficiency of the head. These
factors which include inductance, gap length, core structure, core loss, coil
structure, and copper losses may easily more than offset the advantages
gained by a mere increase of track width.
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Typical record and erase track widths with calculated output levels, based on
track widths, and actual output levels.
record Play Erase Record Erase Calculated Relative Actual
model model track track level output output
no. no. width width relative level level
985 985 0.014 -8.07 -8 +8
1300 1300 0.025 -5.56 -24 -8
975 975 0.028 -5.07 -8 +8
986 986 0.042 -3.30 -8 +8
1500 1500 0.050 -2.55 -14 +2
1090 1090 1110 0.090 0.110 0 0 +16
1091 1091 1110 0.090 0.110 0 +6 +22
815 815 815 0.092 0.118 0 -6 +10
919 919 944 0.118 0.145 +1.18 -8 +8
1250 1250 1252 0.245 0.257 +4.35 +9 +25
* Output levels based on 1 millivolt = 0 db without regard to circuit impedance.
Therefore, they do not indicate real db levels but may be used for comparison
purposes on a voltage basis.
TRACK WIDTH VERSUS ALIGNMENT
Losses due to lateral deviation (azimuth misalignment) become increasingly
significant as the track width is increased. This becomes self-evident if we
again think of a single longitudinally arranged string of magnetic domains
being scanned by a head with a track width equal to one domain. No matter
how the head is laterally deviated, the track will be fully scanned as illustrated
in Figure 11-2 A. A complete 90-degree misalignment will still scan the track
Fig. 11-2A. Scanning of a very narrow track with 45- and 60-degree lateral
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deviations. No but display losses characterized by the lateral scanning of a
longitudinal magnetization. On the other hand, if the same gap is used to scan
a track five times wider appreciable losses result from equivalent lateral
deviation as illustrated in Figure 11-213. The overall effect would be
equivalent to a loss of high frequencies. Narrow gap heads, which are
necessary for extended high frequency response at slow tape speed, require
critical lateral alignment when used with wide tracks.
Misalignment need not necessarily occur only through improper head
mounting but may also be effectively produced by oversized or worn tape
guides, subnormal tape widths, improper capstan-pressure roller alignment
and, in fact, any mechanical deficiency I in the mechanism which fails to hold
the tape in a fixed and consistent relationship to the head gap.
Variation in output level caused by lateral deviation between that equivalent
lateral deviations produce greater losses on a wider head and tape may be
estimated from Figure 11-3. It can be seen track.’ For example, a i-mit
wavelength on a 90-mil track scanned with a deviation of 1/6 of one degree
loses 1.5 db. An equivalent deviation on a 240-mil track exhibits a loss of 8.75
The idea of multiple recording tracks on a single tape is by no means new, as
a multiplicity of systems of this nature have previously been employed with 8,
16, and 35mm films. Since the magnetic track width is not too critical (there
are both advantages and disadvantages
for making the track width either too wide or too narrow) the adaptation of
multiple tracks to magnetic recordings was a natural consequence of attempts
to cut tape costs.
A dual-track system, with automatic reversal at the end of tape travel (or the
reel crossing method), provides the perfect means for eliminating tile
necessity for rewinding by utilizing two magnetic tracks on standard 1-inch
tape, so that the second track is played (or recorded) in the reverse direction,
while the original t is being simultaneously rewound. Advantages of this
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system include doubled playing time from a given length of tape which, in
effect, cuts tape costs in half.
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Capacity and production
1 Total licensed capacity 17300 MRM of ¼ “
2 Total installed capacity 11150”
3 Likely target of production 7200”
4 Average capacity utilization 64%
(Source : DOE and Industrial Units Field Survey)
Figures of audio domestic grade demand :
1 1990 1991 1992
2 Audio tape in 19985 23982 28778
MRM of ¼
3 In millions of 370 443 532
(Source : MMSA field survey)
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Item Quantity in lac Value in Rs. Quantity value
(1987) lac (01)
1 Audio 5.1 80.6 7.7 102.3
2 Pre 9.9 142.8 12.6 185.6
Import of Tape:
As at present there is a limited import of domestic grade audio tape. However
there is large scale import of professional grade audio tape. Though no
official segregated figures are available, it is considered that total import bill is
in excess of US $ 20 million.
Sources of Technology
1 Singapore Tony, Hong electromagnetics
2 Hong Kong Swilyn, Acme Tapes, Casin Cassetetes, MCL
3 USA Magna-tek, CRI, Independent Machienes, Dupont and
4 Japan OKURA & Co., Unitech
5 UK Zonal ltd.
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International Producers of Magnetic Tapes
S.No MANUFACTURER COUNTRY BRAND
1 Fujifilm Japan Fuji
2 Hitachi Maxwell Japan Maxwell
3 Sumitomo Japan 3M
4 Sony Japan Sony
5 TDK Japan TDK, AKAI
6 Victor Magnetics Japan Victor
7 Panasonic Japan Panasonic
8 AGFA Germany AGFA
9 BASF Germany BASF
10 Ampex USA Ampex
11 Memorex USA Memorex
12 Scotch-3M USA Scotch / 3M
13 Kodak USA Kodak
14 Polaroid USA Polaroid
15 RCA USA RCA
16 Sunkyong S.Korea SKC
17 Lucky Goldstar S.Korea Lucky
18 Graham Magnetics USA Graham
Japanese companies are enjoying a very large share of the world market. It is
estimated that 65% of the share is with Japan, 10 % with Korea and the
balance with other countries.
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Formal collaboration agreements exist only in the case of sushmit sangeeta,
Tony, Pan tape. Also the agreement of Gunware and HPF cover audio tape.
The exports are being made as follows :
a) Tony : USA, UK, Singapore, Middle East, Romania etc.
b) Weston : USA, Canada, UK, Singapore, and Hong Kong.
Most of the exports are related to Indian software pre recorded tapes. The
sale is also to countries having Indian non resident population. The
constraints are :
a) Non standard tape production not certified as conforming to ISI.
b) No economy of scale.
c) Price competion from bulk producers.
The demand of audio cassettes in the country is booming.
Rs . in crore
1 Basic magnetic tapes 15 % 77
2 Value added by loading into C-O 20 % 103
3 Value added by recording 45 % 232
4 Wholesale and retail gross 20 % 103
5 Sub total 100 % 515
(Source: Business India – Issue No. 218)
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Possible process gaps
a) Know – why : The most vital gap is the absence of know – why . the
knowledge of various functions to the workers is not sufficient at all for the
manufacturing of quality products. That’s why India is trailing in terms of
quality of products as compared to other countries of the world.
b) Slurry formulation : An important gap is non-appreciation of the importance
of slurry formulation and preparation. This is evident from the fact that most
plants are placing a lot of stress on Q.C for magnetic tape but hardly any
expenditure is done for this purpose.
c) Coating Thickness : one of the parameters of good tape is precise control
within fine tolerances of the coating thickness over the base tape. Irrespective
of what system of coating is employed highly expensiv enuclesr thoickness
Gauges are employed fto messure the thickness and later on control
equipment to correct the defect and keep it within the permissible tolerance.
d) Cleanliness in manufacture: This has two aspects. One is environmental
cleanliness. The second aspect which is neglected is the tape cleaning
system. In good plants these are employed particularly at two places :-
Before and during Slitting
e) Quality Control : Despite standard equipment for drop out test , the quality of
the tape in the market is widely varying. The Q.C system has to be based on
scientific sampling, after giving due considerations to the various stages of
process, to ultimately supply predictable quantity data for each batch on which
the production can be classified.
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Gaps in capital goods
a) Mill Room : The mixing equipment and process are designed to produce a
dispersion of magnetic oxide in a solvent solution and catalysts activated
resins. The two major critical elements of capital goods where possible gaps
Hi-shear Dissolvers: Must have explosion proof design with automatic
speed control. Vaccum accessory desireable. Should be easy to change
Sand Mills : Four bank sand mills with microprocessor control to maintain
correct product temperature and flow rate. Water cooled mills with a
continuous blending system attached at the end of the cycle.
b) Coating Machine : All coaters installed so far, are 13 inch width low speed
machines of the basic type. The latest coaters would have the following
Two shaft turret unwind
Flying splicer at both ends
200 mpm, 26 inch width high speed coaters, gravure roll or reverse roll
Web cleaning and anti static bars
High quality coating thickness gauging systems
Pin hole and asperity detection by laser eye
Microprocessor control, monitoring and data logging specially for drying tunnel
air flow and temperature control.
c) Calendars : 26 inch, high speed calendars with 7-9 rolls. Adjustable D.C
drives, with electrical heating units and chilled water chill rolls. Two shaft turret
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d) Slitters : High speed 200 mpm, high volume production slitters with precise
tension control for webs. Two shaft turret unwind with a splice station.
Needs for extension of technology
There is certainly a need for up gradation of formulation technology for
catering to higher grades of tapes.
a) All out efforts should be made to encourage development of indigenous
input materials. Initially audio tape demands should be met and later on
the demands of the more stringent Video Tapes Specifications. The
two major materials are Polyester Film and Ferric Oxide.
b) As far as Gamma Ferric Oxide is concerned this is required for audio
tapes. This has a growing demand and its production should now be
taken up in India.
c) ETTDC should set up special evaluation facility for V-O and C-O
cassettes and only approved cassettes should be allowed to be used.
Slurry Formulation Department
a) Work to be undertaken fro development of slurry formulation to
compensate for different material inputs.
b) Development of slurry formulations to ensure higher grade of coatings .
c) Original work for development of DAT, DVT, Super VHS or other
multilayer coatings as also changes required in coasting methods for
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d) Development of slurries for high speed coating of say 200 mpm which
is being done outside.
Development of Coating Technology :
There are two developments which can have a direct bearing on viability and
profitability of the Indian plants. Firstly more sophisticated spooling
arrangements have been developed to avoid butt roll change over time.
These Flying Splice machines can mean higher productivity from the same
capital equipment. Secondly coating machine speeds are increasing, which
can improve the productivity.
Development of Manpower
It is found that where as there are large number of people in mechanical,
electrical and electronic disciplines, there is a shortage of manpower in the
chemical and the maintenance fields. In the chemical field it would be
necessary to stress on the development of specialized manpower for slurry
preparation and quality control. In the maintenance area, the requirement is to
train manpower to maintain coating / calendaring / slitting systems.
CONCLUSIONS AND RECOMMENDATIONS
The Magnetic Tape industry has grown very rapidly over the last few years. It is
expected to cross Rs. 1020 crores by 2010.
The technology for manufacture of Magnetic Tapes has not yet come of age in
the country. India is buying technology from other countries but it will still take
time to reach to its full potentials.
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It is also a fact that Indian market is very cost conscious and demand for higher
grade products at even marginally higher cost is not developed. However it
should be emphasized that with careful up gradation of technology , it should be
possible to produce a better quality at the present price levels itself.
Yet another constraint in obtaining quality is the minimum configuration
machines purchased by the Indian project. In this area deeper study by the
industry is needed for up gradation.
Also research and development inputs are required for the development of
indigenous technology. This technology can be broadly classified as under :
b) Solvent Chemistry
d) Production Technology
In general, despite non standard quality , the industry has rendered valuable
service in saving foreign exchange and that too in almost a Free Trade
environment wherein foreign makers are easily available. Under these
circumstances the industry deserves calculated protective measures to
encourage present efforts without compromising consumer interests.
Research and Development
Government should take action to nominate a laboratory like NCL to
undertake development of “Know-why”, specifically in the areas of slurry
formation and coating technology. Sufficient funds should be placed at their
disposal so that the existing audio technology can be upgraded.
The industry has become so large that now consumer protection is a
must. The manufacturer of the end product – blank or pre recorded,
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must be made to state the quantity of the tape and the quantity time of
It is recommended that BIS revises standard for audio cassettes.
BIS should also publish the test method to meet the standards and
establish test facilities for the same.
Test facilities should be provided .
Raw Materials Import
Government must encourage the development of sources for indigenous raw
Polyester Film, and
Gamma Ferric Oxide
Capital Goods Import
Even though certain machines have been developed for audio tapes, it is
found that these are minimum configuration machines and it may not be
possible to use them for higher quality products. Therefore it is felt that for the
present the machinery for audio tape will have to be imported. However
development efforts must continue to improve the machines.
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