Compact Discs and CD Players

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					CDs and CD Players


Compact discs and CD players

Ben Hu Michael Ho Rahul Patel
Optical Engineering Dr. Kasra Daneshvar July 17th, 2004

CDs and CD Players Abstract: Compact discs, or CDs, are present everywhere in our lives. Millions, if not billions, of people use them every day in applications ranging from communication to


entertainment to medicine. As widely used as CDs are, relatively few people know how they work, how they are manufactured, or how they are read. Knowing this information would be extremely useful and would provide insight into how to solve everyday problems involving CDs and CD-reading equipment. The purpose of this research was to learn about how CDs work, how they are read, the equipment that is used to read and write them, and the different kinds of CDs. The research was conducted by using information from published sources to answer these questions. A brief summary of how CDs work is that a spiral of microscopic bumps is impressed on the CD during manufacturing. A CD player uses a laser to read these bumps, which act as ones and zeroes, to create a digital signal, which is then converted to an analog signal that is received by the user. This report will disclose more detailed information regarding CDs and CD players.

CDs and CD Players Background:


Development on the CD first began in the early 1970s. After about ten years of testing, development, and standardization, Sony and Philips sold the first CDs to the public during the fall of 1982. Demand was slow at first, but with the introduction of CD-ROM drives to the computer market, sales picked up quickly. The large amount of data storage space and ease of use made it a winner over cassettes and floppy disks, but cost remained a problem. As CD prices dropped, sales overtook those of other data storage devices and only increased with the appearance of CD-Recordable (CD-R) discs in 1991. Digital Versatile Discs (DVDs) were released in 1997, and with the movie industry utilizing DVDs, the CD/DVD industry soared.

CDs and CD Players Compact discs and CD players In less than thirty years, a small circular piece of plastic the size of one’s hand has completely revolutionized the world. Because of their data-storing capabilities, portability, and cost-effectiveness, compact discs have been used in all kinds of applications, ranging from entertainment to business to military uses. The electronics and software industries have both experienced major growth due to compact disc technology. CDs can now be found in almost every household in the United States and other developed countries. CD players have also changed the world to a lesser extent; the first means of being a portable CD reader, they have become a near necessity to the teenaged population. CDs and CD players may be worldwide now but they are still made the same way no matter where the location is. Conventional CDs are 4.8 inches wide and can hold about 783 megabytes of information on them, which is about 74 minutes of audio (Brain, 2000). Even though it seems complex, a CD is mainly made of simple polycarbonate plastic. This plastic is


manufactured with millions of microscopic indentions, or bumps, arranged in one single, continuous spiral of data on the CD. A layer of aluminum is then molded onto the plastic, covering the indentions, and is then protected by acrylic and the label of the CD. The single most important part of a CD though is not the plastic itself, but the indentions on it. As previously stated, these bumps form a single spiral on the CD. This spiral is extraordinarily small, 0.5 microns wide and 1.6 microns separating each line of the spiral from the next (Brain, 2000). Thus the indentions are much smaller than that, seeing as how millions of them make up the spiral. In fact, they are 125 nanometers

CDs and CD Players high (one-billionth of a meter). These bumps are the very data that the CD holds, each single bump doesn’t particularly matter but the series that they are in is what counts. The order of the indentions is extremely important, as it will determine what the CD player will transmit when reading it. A CD player is made up of three basic parts: a drive motor which spins the disc, a laser and lens system which reads the indentions, and a tracking mechanism which


keeps the laser on the spiral (Brain, 2000). The tracking mechanism must work with the drive motor in unison at all times. They work together to keep the laser moving outwards and on the spiral, and keep the indentions passing the laser at the same speeds. As the tracking motor moves the laser outward the indentions pass the laser faster, thus the drive motor has to slow the RPM constantly at specific points and exact times. It is necessary to keep the data flowing at a constant rate, otherwise the music will come out too fast or too slow and become indistinct. After all of that is in equilibrium then the information can be correctly read by the laser and transmitted out in digital form. The laser’s task is to enter the plastic layer of a CD and relay its “findings” to an optical pickup device located near it. To do this the laser beams a constant light through the plastic (hitting any bumps on the way) and is reflected back by the aluminum layer. Upon arrival, the optical pickup device reads this constant beam and acquires data. When the laser hits a bump, the light fluctuates, causing a different reflection. The pickup device interprets this change in reflection and transmits a one. When there is no indention and the laser passes and is reflected clearly, it transmits a zero. All of this is done at extremely high speeds [The disc rotates from 500-350 RPM (Brain, 2000)] so the pickup device transmits a continuous amount of zeroes and ones, known as a digital

CDs and CD Players signal. This digital signal is sent to the headphones or other output device and is


converted to an analog signal, which is more extensive. It is converted because a digital signal is impossible for humans to comprehend, but an analog signal is understandable. After the signal is converted by a Digital-Analog-Converter inside the headphones, the analog signal must be amplified to be heard. An amplifier is placed inside the headphones, usually near earpieces, and out comes sound. Even though this process may seem lengthy, the whole thing takes place almost instantaneous. A CD player has its limitations though, and can only read certain types of CDs. There are several different types of compact discs, each following the same basic principle, but also varying in some ways. The two main different types of CDs are CD-Recordables and CD-Rewriteables. Unlike CDs, CD-Recordables have no indentions. Instead they are coated with a clear, light-sensitive dye layer. A write laser, also known as a CD Burner, burns specific microscopic sections of this dye layer, turning it from clear to opaque. These opaque sections are read the same way as the indentions, by different reflectivity, so all CD-Rs can be read by any conventional CD player. CD-RWs on the other hand are a bit different; instead of a dye layer or indentions they are covered with a clear, crystalline compound. This crystalline compound has a few special properties, most importantly the ability to change from opaque to transparent and vice-versa at different temperatures. With a CD-RW there must be a write laser, a read laser, and an erase laser, each one having a different power to change the state of the CD; therefore only specialized CD players can read these.

CDs and CD Players Another evolution of the CD is the Digital Versatile Disc, also known as a DVD. There are some similarities and differences between CDs and DVDs. The physical attributes between CDs and DVDs are identical, but a DVD can store seven times as much information as a CD. A DVD is capable of this because it has a slightly tighter spiral track and smaller bump size allows for four and a half times as many bumps as CDs. Also, a DVD utilizes a more efficient error correction scheme that allows for more space on the DVD for real information. Double layers on a DVD allow for even more storage capacity, with each layer able to hold as much as 4.7 gigabytes.


Conclusion: The future may hold bright things for compact discs. Someone down the road may invent a way to connect one’s brain to a device containing a CD, and be able to record and store one’s thoughts and dreams onto a CD. This would be an effective way to help people to remember their dreams and thoughts. Even if this doesn’t happen, CDs will most likely always be around as a good, if not the best way, to store information at a cheap price. From being able to store audio, video, and information to holding extensive games and movies, the compact disc has greatly impacted the modern world in a way that people twenty years ago couldn’t have imagined.

CDs and CD Players References: Brain, M. (2000). How CDs Work. How Stuff Works.


Davidson, M. (2001) History of the Compact Disc. Molecular Expressions.

Hui, T. & Tang, Y. (2000) Compact Discs (CDs). Instructional Computing.

Despain, J. (1999) History of CD Technology. OneOff Media, Inc

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