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The CD player Technology To the main menu click here To return to the Hutman Museum of Sound click here |
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The CD player Technology To the main menu click here To return to the Hutman Museum of Sound click here |
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 How CD's Work A CD can hold 74 minutes of music. This is how the total of digital data is calculated: 44,100 samples/channel/second x 2 bytes/sample x 2 channels x 74 minutes x 60 seconds/minute = 783,216,000 bytes To do this individual bytes must be small. A CD is a piece of plastic. It is four one-hundredths (4/100) of an inch (1.2 mm) thick. It is in fact injection-molded clear polycarbonate plastic. The plastic is impressed with microscopic bumps put on as one continuous, extremely long spiral track of data. A thin, reflective aluminum layer is sputtered on the disc. It covers the bumps. Next a thin acrylic layer is sprayed over the aluminum. The label is then printed onto this acrylic layer. The spiral track of data begins at the center. This makes the CD able to be smaller than 4.8 inches (12 cm) if necessary. The data track is very small. It is only 0.5 microns wide. 1.6 microns separate tracks from one another the next. The bumps are much smaller. The elongated bumps that make up the track are each 0.5 microns wide, a minimum of 0.83 microns long and 125 nanometers high. (A nanometer is a billionth of a meter.) Looking through the polycarbonate layer at the bumps, they look something like this: The bumps on the cd are pits on the aluminum side, On the side the laser reads they form bumps. Because the bumps are so small the spiral track on a CD very long. The data track of a CD stretched out straight would be 0.5 microns wide and about 3.5 miles (5 km) in length. The reading mechanism for such a small data track must be very exacting. The CD player has to find and read the data. That is it reads the bumps . The drive has three parts. The drive motor moves the disc. It rotates from 200 to 500 rpm. A laser and a lens mechanism focus on the bumps and and reads them. . The tracking mechanism moves the laser along the spiral track. The tracking system moves the laser in micron increments. Computer technology turns the recorded data into meaningful data and sends it them to the DAC in an audio player or to the computer attached to a CD drive. The CD player is to focuses the laser bumps. The beam passes through the polycarbonate layer but reflects off the aluminum layer then it hits an opto-electronic mechanism that picks up changes in light. The bumps reflect light differently than other portions of the aluminum layer. The sensor detects the changes in reflectivity. The drive then interprets the changes as bits that make up the bytes thus translating them into meaningful information data or songs. There are many ways of interpreting the data.
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Chronology 1841 Augustin-Louis Cauchy Proposes a Sampling Theorem. 1842 Charles Babbage Proposes analytical engine for performing and storing calculations. 1854 George Boole publishes "An Investigation Into the Laws of Thought." A book that contained, among other things, theories that were later used to build digital circuits. 1855 Leon Scott de Martinville invents the phonoautograph, a machine that records vibrations on a carbonized paper cylinder. 1876 Alexander Graham Bell introduces the telephone 1877 Thomas Edison invents the phonograph while trying to invent a device that would record and repeat telegraphic signals (digital) 1887 Emily Berliner replaces Edison's wax cylinder phonograph with the audio disc. 1915 78 R.P.M records introduced 1922 J.R. Carson examines the idea of time sampling for communications 1928 Harry Nyquiest publishes "Certain Topics in Telegraph Transmission Theory." His theory contained proof that the technology used in todays audio cd's could work. 33 1/3 Records Introduced 1937 A. Reeves invents pulse code modulation (PCM), a technology used by computers and CD's for audio in the present day. H. Aiken from Harvard approaches IBM and proposes a electrical computing machine. 1943 The U.S. Army turns on the first computer (ENIAC) at the University of Pennsylvania. 1947 Magnetic Tape Recorders hit the U.S. market. 1948 The transistor is invented by Bell Laboratories. Claude E. Shannon publishes "A Mathematical Theory of Communication." -- Yet another important development for theories used in CD technology 1949 45 rpm records hit the U.S. market, thanks to microgroove technology. 1950 Richard W. Hamming publishes information about error detection/correction codes. It would be impossible for CD's to work without error correction. 1958 Invention of the Laser. Stereo LP's produced. Integrated Circuit introduced by Texas Instruments 1960 Computer Music experiments take place at major laboratories. I.S. Reed and G. Soloman publish information on multiple error correction codes. These come to be known as the "Reed-Solomon" Codes which are the codes used for encoding and reading CD's. Working Laser produced. 1967 NHK Technical Research Institute demonstrates a 12-bit PCM digital audio recorder with a 30 kHz (30,000 times per second) sampling rate. The digital recording goes onto a high-grade video tape. 1969 Sony introduces it's 13-bit PCM digital recorder at a 47.25 kHz (47,250 time per second) sampling rate. The digital recording is sent to a 2" video tape. Klass Company, a Dutch physicist comes up with the idea for the Compact Disc. 1970 At Philips, Company and Pete Kramer complete a glass disc prototype and determine that a laser will be needed to read the information. 1971 Microprocessor produced by Intel Digital Delay line used by BBC's studios (first digital audio device). 1972 Compaan and Kramer produce color prototype of this new compact disc technology 1973 BBC and other broadcast companies start installing digital recorders for master recordings. 1977 Mitsubishi, Hitachi & Sony show digital audio disc prototypes at the Tokyo Audio Fair. JVC Develops Digital Audio Process 1978 Philips releases the video disc player Sony sells the PCM-1600 and PCM-1 (digital audio processors) "Digital Audio Disc Convention" Held in Tokyo, Japan with 35 different manufacturers. Philips proposes that a worldwide standard be set. Polygram (division of Philips) determined that polycarbonate would be the best material for the CD. Decision made for data on a CD to start on the inside and spiral towards the outer edge. Disc diameter originally set at 115mm. Type of laser selected for CD Players. 1979 Prototype CD System demonstrated in Europe and Japan. Sony agrees to join in collaboration. Sony & Philips compromise on the standard sampling rate of a CD -- 44.1 kHz (44,100 samples per second) Philips accepts Sony's proposal for 16-bit audio. Reed-Solomon code adopted after Sony's suggestion. Maximum playing time decided to be slightly more that 74 minutes. Disc diameter changed to 120mm to allow for 74 minutes of 16-bit stereo sound with a sample rate of 44.1 kHz 1980 Compact Disc standard proposed by Philips & Sony. 1981 Matsushita accepts Compact Disc Standard Digital Audio Disc Committee also accepts Compact Disc Standard. Sharp achieves production of semiconductor laser. Philips & Sony collaboration ends. 1982 Sony & Philips both have product ready to go. Compact Disc Technology is introduced to Europe and Japan in the fall. 1983 Compact Disc Technology is introduced in the United States in the spring The Compact Disc Group formed to help market. CD-ROM Prototypes shown to public 30,000 Players sold in the U.S. 800,000 CD's sold in the U.S. 1984 Second Generation & Car CD players introduced. First Mass Replication Plant in the United States built. Portable (i.e., Sony Disc Man) CD Players sold. 1985 Third generation CD Players released. CD-ROM drives hit the computer market. 1986 CD-I (Interactive CD) concept created. 3 Million Players sold in U.S. 53 Million CD's sold in U.S. 1987 Video CD format created. Allen Adkins of Optical Media International joins with SonoPress in Amsterdam and demonstrates a desktop system for pre-mastering CD's (Adkins and SonoPress, produced a replicated CD in less than 24-hours using this system). 1988 CD-Record able Disc/Recorder Technology Introduced 1990 28% of all U.S. households have CD's. 9.2 million players sold annually in the United States. 288 million CD's sold annually in the United States. World Sales close to 1 Billion 1991 CD-I format achieved. CD-Record able Introduced to the Market "Quick Topix" the first CD-R pre-mastering Software introduced by Allen Adkins. 1992 CD-R Sales reach 200,000 1996 DVD Technology Introduced. Prices of Recorders and CD-R Media go down significantly. High Demands cause World-Wide CD-R Media Shortage. 1997 DVD Released. DVD Players/Movies hit consumer market. DVD-R standard created (3.9 Gig). Mitsui builds it's first CD-R production plant in the U.S. World-wide shortage ends. Price of CD-R media lower than ever imagined. 1998 DVD-RAM, DVD- Record able systems/equipment hits market. DVD-Video/ROM authoring tools hits the market. CD-R prices continue to drop. 1999 DVD-Video Becomes main stream. Consumers begin purchasing DVD Players & Movies on a mass level. Most major film studios have titles on DVD. DIVX Dies (DIgital Video eXpress). Second Generation DVD Burners. 4.7 Gig DVD-R Media Developed. Source 1841-1991 Pohlmann, Ken C. "The Compact Disc Handbook, 2nd Edition" |
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| History of the Period
Computers, technology |
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| Activity Record or find an unwanted audio compact cassette tape Place a magnet next to the tape Play play the tape. Do the same for a CD Play the cd Cover your eyes. Have someone play an unscratched high fidelity LP Next have someone play a cd Could you tell the difference? Was the sound better or just different? Which was richer sounding. Why was it that CDs could not originally be recorded? Can you record an LP? Which is easier to play safely while driving in a car- LP, 8track, CD, Compact Cassette? How does the CD reflect a mobile, homeless and car less consumer? |
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Restoration and Parts Assistance
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Tour of My CD Player
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Mechanism |
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Inserting the cd |
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View of mechanism |
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Cd ready to begin to play |
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