EE3104 Digital Sound and Music Production

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EE3104 Digital Sound and Music Production Powered By Docstoc
					         EE2215:
Sound & Music Production for
        Broadcast


     MIDI, Timing
         and
    Synchronisation
     MIDI; Musical Instrument
         Digital Interface
• “idea of industrial standard” discussed at
  National Association of Music Merchants
  (American association) [summer 1981]
• “Universal Synthesizer Interface” proposed at
  Audio Engineering Society [winter 1981]
• initiative passed to Japan. a group of
  manufacturers including Casio, Kawai, Korg
  and Yamaha, with Sequential Circuits (USA)
  [1982]
• MIDI specification announced [1983]
   MIDI Specification 1.0. (1983)

computer:
  8-bit CPU, 8 MHz clock
  with 32k-byte memory
CD:
  16-bit, 44.1 kHz (1982)
MIDI:
  8-bit code, 31.25 k bps
             After MIDI (1)
Present technology
  computer:
     64-bit CPU, 4 GHz clock
     with 8 GB memory
  game machine:
     128-bit CPU
     >> magnitudes difference in 20 years
             After MIDI (2)

General MIDI system (1991)
 "minimum" compatibility in MIDI

ZIPI (1994)
  an attempt to replace MIDI
  made by American academics
      without industrial supports
      no hardware implementation
             After MIDI (3)

problems on MIDI system
  hardware limitations;
      communication speed
      maximum length of “chain”
      8-bit system
           After MIDI (4)

ad-hoc solutions:
   multi-cable MIDI on PC
   long-distance transmission with PCs
   word-length and transmission speed
        in the latest PC standard
  Timing Measurement (1)



MIDI Time Code (absolute timing)
  hh : mm : ss : frame : ¼ frame

Metronome (relative timing)
 bar : beat : tick
 << beat per minutes
 << tick per ¼ note
   Timing Measurement (2)
MIDI Time Code (absolute timing)
 SMPTE video code based
 hh : mm : ss : frame : ¼ frame

  minimum timing
  PAL system
   - 25 frames per sec. >> 1/25 sec (40 msec)
   with ¼ frame message >> 1/100 sec (10
   msec)
    Timing Measurement (3)
Metronome (relative timing)
  musical timing based
  bar : beat : tick
       << beat per minutes
       << tick per ¼ note
       4/4 with 240 beats
              (240 x ¼ notes) a minute
       = 4 beats a sec
       with 25 ticks per ¼ note
              >> 1 tick = 1/100 sec (10 msec)
   Timing Measurement (4)
What 1/10 sec (100 msec) means…
  PAL 25 frames per second
   - 1/25 sec (40 msec) per frame >> 2.5
   frames
  CD quality sound 44.1 kHz sample rate
   - 4410 samples
  Sound travels 320 m per second
   - 32 m       i.e. echo from 16 m away
  Timing : human perception
The timing between two clicks…
 1 / 100 sec (10 msec)
     musicians
 1 / 50 sec (20 msec)
     sensitive listeners
 1 / 30 sec (33.3 msec)
     most of listeners
        MIDI communication
              content
The information that MIDI carries;
  – which notes are pressed/ released
  – which controls are used;
      pitch bend, vibrato, pedals, wheels
  – MIDI time code;
        absolute time reference
  – tempo information
  – instrument information
        MIDI communication
             format (1)
MIDI communication is 8-bit based contents
  with one start-bit and one end-bit; 10-bit
  communication.

8-bit contents (0 – 255) usually described in 2
  digits of Hexadecimal number.
  hex 0 1 2 3 4 5 6 7 8 9 A B C D E F
  dec 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
       60 (10) = 3C (16) or 3C (hex)
        MIDI communication
             format (2)
Format: one status-byte followed by two data-
  bytes.

status-byte (80(hex)-FF(hex))
  function (note_on, note_off…)
  channel information
data-bytes (00(hex)-7F(hex))
  data value
        MIDI communication
            format (3)
one “note_on” event :
  90             3C             40
  <status byte> <key number> <velocity>
  90 note_on at channel 0
  3C middle C
  40 strength: medium
        MIDI communication
             format (4)
one “note_off” event :
  80              3C            40
  <status byte> <key number> <velocity>
  80 note_off at channel 0
  3C middle C
  40 <no meaning>
        MIDI communication
             format (5)
one “note_off” event using “note_on”:
  90              3C              00
  <status byte> <key number> <velocity>
  90 note_on at channel 0
  3C middle C
  00 “0” velocity -- no sound

                             >> running status
        MIDI communication
            format (6)
running status:
  “status byte” will be sent ONLY contents of
  “status byte” changes

90 3C 40 40 40 43 40 3C 00 40 00 43 00

90 3C 40 90 40 40 90 43 40
80 3C 00 80 40 00 80 43 00
     MIDI communication size

120 key strokes…
120 x 2 (events) x 10 (bits) x 3 = 7200
  (bits)
= 900 (bytes)
      slightly less than 1 kB

NB   1 K Byte = 1024 (210) Bytes
     1 Byte = 8 bits
     MIDI communication
speed and number of connection
• MIDI communication speed 31.25 kbps
• one note-on event (30 bits) needs about one
  milli-second (msec) to be transmitted.
• Human ears can detect 10 msec difference.
• Opto-Isolator at MIDI-IN port gives 2 – 4
  msec delay.
• MIDI Spec 1.0 restricts a maximum of 5
  hops.
        MIDI communication
             summary
Generally MIDI files do not carry any sound
 information, as the sound is generated by
 sound cards or MIDI sequencing software
 that have the sound source – MIDI sound
 ROMs or “sound fonts”. Hence, different
 software/sound card may generate different
 sound. >> General MIDI

				
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posted:4/7/2010
language:Spanish
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