Compact disc facts for kids
Compact disc (CD) is a digital optical disc data storage format released in 1982 and co-developed by Philips and Sony. The format was originally developed to store and play only sound recordings but was later adapted for storage of data (CD-ROM). Several other formats were further derived from these, including write-once audio and data storage (CD-R), rewritable media (CD-RW), Video Compact Disc (VCD), Super Video Compact Disc (SVCD), Photo CD, PictureCD, CD-i, and Enhanced Music CD. The first commercially available Audio CD player, the Sony CDP-101, was released October 1982 in Japan.
Standard CDs have a diameter of 120 millimetres (4.7 in) and can hold up to about 80 minutes of uncompressed audio or about 700 MiB of data. The Mini CD has various diameters ranging from 60 to 80 millimetres (2.4 to 3.1 in); they are sometimes used for CD singles, storing up to 24 minutes of audio, or delivering device drivers.
Contents
History
American inventor James T. Russell has been credited with inventing the first system to record digital information on an optical transparent foil that is lit from behind by a high-power halogen lamp. Russell's patent application was first filed in 1966, and he was granted a patent in 1970. Following litigation, Sony and Philips licensed Russell's patents (then held by a Canadian company, Optical Recording Corp.) in the 1980s.
The compact disc is an evolution of LaserDisc technology, where a focused laser beam is used that enables the high information density required for high-quality digital audio signals.
Prototypes were developed by Philips and Sony independently in the late 1970s. Although originally dismissed by Philips Research management as a trivial pursuit, the CD became the primary focus for Philips as the LaserDisc format struggled. In 1979, Sony and Philips set up a joint task force of engineers to design a new digital audio disc. After a year of experimentation and discussion, the Red Book CD-DA standard was published in 1980.
After their commercial release in 1982, compact discs and their players were extremely popular. Despite costing up to $1,000, over 400,000 CD players were sold in the United States between 1983 and 1984. By 1988 CD sales in the United States surpassed those of vinyl LPs, and by 1992 CD sales surpassed those of prerecorded music cassette tapes. The success of the compact disc has been credited to the cooperation between Philips and Sony, who came together to agree upon and develop compatible hardware. The unified design of the compact disc allowed consumers to purchase any disc or player from any company, and allowed the CD to dominate the at-home music market unchallenged.
Collaboration and standardization
Sony executive Norio Ohga, later CEO and chairman of Sony, and Heitaro Nakajima were convinced of the format's commercial potential and pushed further development despite widespread skepticism.
As a result, in 1979, Sony and Philips set up a joint task force of engineers to design a new digital audio disc. Led by engineers Kees Schouhamer Immink and Toshitada Doi, the research pushed forward laser and optical disc technology. After a year of experimentation and discussion, the task force produced the Red Book CD-DA standard. First published in 1980, the standard was formally adopted by the IEC as an international standard in 1987, with various amendments becoming part of the standard in 1996.
Philips coined the term compact disc in line with another audio product, the Compact Cassette, and contributed the general manufacturing process, based on video LaserDisc technology. Philips also contributed eight-to-fourteen modulation (EFM), which offers a certain resilience to defects such as scratches and fingerprints, while Sony contributed the error-correction method, CIRC.
The Compact Disc Story, told by a former member of the task force, gives background information on the many technical decisions made, including the choice of the sampling frequency, playing time, and disc diameter. The task force consisted of around four to eight persons, though according to Philips, the compact disc was "invented collectively by a large group of people working as a team."
Initial launch and adoption
Philips established the Polydor Pressing Operations plant in Langenhagen near Hannover, Germany, and quickly passed a series of milestones.
- The first test pressing was of a recording of Richard Strauss's Eine Alpensinfonie (An Alpine Symphony) played by the Berlin Philharmonic and conducted by Herbert von Karajan, who had been enlisted as an ambassador for the format in 1979.
- The first public demonstration was on the BBC television program Tomorrow's World in 1981, when the Bee Gees' album Living Eyes (1981) was played.
- The first commercial compact disc was produced on 17 August 1982. It was a recording from 1979 of Claudio Arrau performing Chopin waltzes (Philips 400 025-2). Arrau was invited to the Langenhagen plant to press the start button.
- The first popular music CD produced at the new factory was The Visitors (1981) by ABBA.
- The first 50 titles were released in Japan on 1 October 1982.
The Japanese launch was followed in March 1983 by the introduction of CD players and discs to Europe and North America (where CBS Records released sixteen titles). This event is often seen as the "Big Bang" of the digital audio revolution. The new audio disc was enthusiastically received, especially in the early-adopting classical music and audiophile communities, and its handling quality received particular praise.
As the price of players gradually came down, and with the introduction of the portable Discman the CD began to gain popularity in the larger popular and rock music markets. One of the first CD markets was devoted to reissuing popular music whose commercial potential was already proven. An advantage of the format was the ability to produce and market boxed sets and multi-volume collections.
The first artist to sell a million copies on CD was Dire Straits, with their 1985 album Brothers in Arms. The first major artist to have his entire catalogue converted to CD was David Bowie, whose 15 studio albums were made available by RCA Records in February 1985, along with four greatest hits albums. On February 26, 1987, the first four UK albums by The Beatles were released in mono on compact disc. In 1988, 400 million CDs were manufactured by 50 pressing plants around the world.
Further development and decline
The CD was planned to be the successor of the vinyl record for playing music, rather than primarily as a data storage medium. From its origins as a musical format, CDs have grown to encompass other applications. In 1983, following the CD's introduction, Immink and Braat presented the first experiments with erasable compact discs during the 73rd AES Convention.
In June 1985, the computer-readable CD-ROM (read-only memory) and, in 1990, CD-Recordable were introduced, also developed by both Sony and Philips. Recordable CDs were a new alternative to tape for recording music and copying music albums without defects introduced in compression used in other digital recording methods. Other newer video formats such as DVD and Blu-ray use the same physical geometry as CD, and most DVD and Blu-ray players are backward compatible with audio CD.
By the early 2000s, the CD player had largely replaced the audio cassette player as standard equipment in new automobiles, with 2010 being the final model year for any car in the United States to have a factory-equipped cassette player. With the increasing popularity of portable digital audio players, such as mobile phones, and solid state music storage, CD players are being phased out of automobiles in favor of minijack auxiliary inputs, wired connection to USB devices and wireless Bluetooth connection.
Meanwhile, with the advent and popularity of Internet-based distribution of files in lossily-compressed audio formats such as MP3, sales of CDs began to decline in the 2000s. For example, between 2000 and 2008, despite overall growth in music sales and one anomalous year of increase, major-label CD sales declined overall by 20%, although independent and DIY music sales may be tracking better according to figures released 30 March 2009, and CDs still continue to sell greatly.
As of 2012, CDs and DVDs made up only 34 percent of music sales in the United States. By 2015[update], only 24% of music in the United States was purchased on physical media, ⅔ of this consisting of CDs; however, in the same year in Japan, over 80% of music was bought on CDs and other physical formats.
Despite the rapidly declining sales year-over-year, the pervasiveness of the technology remains: Companies are placing CDs in pharmacies, supermarkets, and filling station convenience stores targeting buyers least able to utilize Internet-based distribution.
Awards and accolades
Sony and Philips received praise for the development of the compact disc from professional organizations. These awards include
- Technical Grammy Award for Sony and Philips, 1998.
- IEEE Milestone award, 2009, for Philips only with the citation: "On 8 March 1979, N.V. Philips' Gloeilampenfabrieken demonstrated for the international press a Compact Disc Audio Player. The demonstration showed that it is possible by using digital optical recording and playback to reproduce audio signals with superb stereo quality. This research at Philips established the technical standard for digital optical recording systems."
Physical details
- A polycarbonate disc layer has the data encoded by using bumps.
- A shiny layer reflects the laser.
- A layer of lacquer protects the shiny layer.
- Artwork is screen printed on the top of the disc.
- A laser beam reads the CD and is reflected back to a sensor, which converts it into electronic data
A CD is made from 1.2 millimetres (0.047 in) thick, polycarbonate plastic and weighs 15–20 grams. From the center outward, components are: the center spindle hole (15 mm), the first-transition area (clamping ring), the clamping area (stacking ring), the second-transition area (mirror band), the program (data) area, and the rim. The inner program area occupies a radius from 25 to 58 mm.
A thin layer of aluminium or, more rarely, gold is applied to the surface, making it reflective. The metal is protected by a film of lacquer normally spin coated directly on the reflective layer. The label is printed on the lacquer layer, usually by screen printing or offset printing.
CD data is represented as tiny indentations known as "pits", encoded in a spiral track moulded into the top of the polycarbonate layer. The areas between pits are known as "lands". Each pit is approximately 100 nm deep by 500 nm wide, and varies from 850 nm to 3.5 µm in length. The distance between the tracks, the pitch, is 1.6 µm.
A motor within the CD player spins the disc to a scanning velocity of 1.2–1.4 m/s (constant linear velocity) – equivalent to approximately 500 RPM at the inside of the disc, and approximately 200 RPM at the outside edge. (A disc played from beginning to end slows its rotation rate during playback.)
A CD is read by focusing a 780 nm wavelength (near infrared) semiconductor laser housed within the CD player, through the bottom of the polycarbonate layer. The change in height between pits and lands results in a difference in the way the light is reflected. By measuring the intensity change with a photodiode, the data can be read from the disc. In order to accommodate the spiral pattern of data, the semiconductor laser is placed on a swing arm within the disc tray of any CD player. This swing arm allows the laser to read information from the centre to the edge of a disc, without having to interrupt the spinning of the disc itself.
Integrity
CDs are susceptible to damage during handling and from environmental exposure. Pits are much closer to the label side of a disc, enabling defects and contaminants on the clear side to be out of focus during playback. Consequently, CDs are more likely to suffer damage on the label side of the disc. Scratches on the clear side can be repaired by refilling them with similar refractive plastic or by careful polishing. The edges of CDs are sometimes incompletely sealed, allowing gases and liquids to corrode the metal reflective layer and to interfere with the focus of the laser on the pits. The fungus Geotrichum candidum, found in Belize, has been found to consume the polycarbonate plastic and aluminium found in CDs.
Disc shapes and diameters
The digital data on a CD begins at the center of the disc and proceeds toward the edge, which allows adaptation to the different size formats available. Standard CDs are available in two sizes. By far, the most common is 120 millimetres (4.7 in) in diameter, with a 74- or 80-minute audio capacity and a 650 or 700 MiB (737,280,000-byte) data capacity. This capacity was reportedly specified by Sony executive Norio Ohga in May 1980 so as to be able to contain the entirety of Beethoven's Ninth Symphony on one disc.
This is a myth according to Kees Immink, as the code format had not yet been decided in May 1980. The adoption of EFM one month later would have allowed a playing time of 97 minutes for 120 mm diameter or 74 minutes for a disc as small as 100 mm. The 120 mm diameter has been adopted by subsequent formats, including Super Audio CD, DVD, HD DVD, and Blu-ray Disc. The 80 mm diameter discs ("Mini CDs") can hold up to 24 minutes of music or 210 MiB.
Related pages
| Physical size | Audio Capacity | CD-ROM Data Capacity | Definition |
|---|---|---|---|
| 120 mm | 74–80 min | 650–700 MiB | Standard size |
| 80 mm | 21–24 min | 185–210 MiB | Mini-CD size |
| 80x54 mm – 80x64 mm | ~6 min | 10-65 MiB | "Business card" size |
Manufacture
Replicated CDs are mass-produced initially using a hydraulic press. Small granules of heated raw polycarbonate plastic are fed into the press. A screw forces the liquefied plastic into the mold cavity. The mold closes with a metal stamper in contact with the disc surface. The plastic is allowed to cool and harden. Once opened, the disc substrate is removed from the mold by a robotic arm, and a 15 mm diameter center hole (called a stacking ring) is created. The time it takes to "stamp" one CD is usually two to three seconds.
This method produces the clear plastic blank part of the disc. After a metallic reflecting layer (usually aluminium, but sometimes gold or other metal) is applied to the clear blank substrate, the disc goes under a UV light for curing and it is ready to go to press. To prepare to press a CD, a glass master is made, using a high-powered laser on a device similar to a CD writer. The glass master is a positive image of the desired CD surface (with the desired microscopic pits and lands). After testing, it is used to make a die by pressing it against a metal disc.
The die is a negative image of the glass master: typically, several are made, depending on the number of pressing mills that are to make the CD. The die then goes into a press, and the physical image is transferred to the blank CD, leaving a final positive image on the disc. A small amount of lacquer is applied as a ring around the center of the disc, and rapid spinning spreads it evenly over the surface. Edge protection lacquer is applied before the disc is finished. The disc can then be printed and packed.
Manufactured CDs that are sold in stores are sealed via a process called "polywrapping" or shrink wrapping.
The most expensive part of a CD is the jewel case. In 1995, material costs were 30 cents for the jewel case and 10 to 15 cents for the CD. Wholesale cost of CDs was $0.75 to $1.15, which retailed for $16.98. On average, the store received 35 percent of the retail price, the record company 27 percent, the artist 16 percent, the manufacturer 13 percent, and the distributor 9 percent.
When 8-track tapes, cassette tapes, and CDs were introduced, each was marketed at a higher price than the format they succeeded, even though the cost to produce the media was reduced. This was done because the apparent value increased. This continued from vinyl to CDs but was broken when Apple marketed MP3s for $0.99, and albums for $9.99. The incremental cost, though, to produce an MP3 is very small.
Images for kids
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The pits in a CD are 500 nm wide, between 830 nm and 3,000 nm long and 150 nm deep.
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700 MiB CD-R next to a mechanical pencil for scale
See also
In Spanish: Disco compacto para niños
