| Name | Compact disc |
|---|---|
| Logo | |
| Caption | The readable surface of a Compact Disc includes a spiral track wound tightly enough to cause light to diffract into a full visible spectrum |
| Type | Optical disc |
| Encoding | Various |
| Capacity | Typically up to 700 MB (up to 80 minutes audio) |
| Read | 780 nm wavelength semiconductor laser, 1200 Kb/s (1×) |
| Write | 1200 Kb/s (1×) |
| Owner | Sony, Philips |
| Use | Audio and data storage |
Standard CDs have a diameter of and can hold up to 80 minutes of uncompressed audio (700 MB of data). The Mini CD has various diameters ranging from ; they are sometimes used for CD singles, storing up to 24 minutes of audio or delivering device drivers.
CD-ROMs and CD-Rs remain widely used technologies in the computer industry. The CD and its extensions are successful: in 2004, worldwide sales of CD audio, CD-ROM, and CD-R reached about 30 billion discs. By 2007, 200 billion CDs had been sold worldwide. Compact Discs are increasingly being replaced or supplemented by other forms of digital distribution and storage, such as downloading and flash drives, with audio CD sales dropping nearly 50% from their peak in 2000.
Sony executive Norio Ohga, who later became the CEO and chairman of Sony, was convinced of the format's commercial potential, and pushed further development despite widespread skepticism. Later in 1979, Sony and Philips Consumer Electronics (Philips) set up a joint task force of engineers to design a new digital audio disc. Led by Kees Schouhamer Immink and Toshitada Doi, the research pushed forward laser and optical disc technology that began independently by Philips and Sony in 1977 and 1975, respectively. told by a former member of the taskforce, gives background information on the many technical decisions made, including the choice of the sampling frequency, playing time, and disc diameter. The taskforce consisted of around four to eight persons, though according to Philips, the Compact Disc was thus "invented collectively by a large group of people working as a team."
The first test CD was pressed in Langenhagen near Hannover, Germany, by the Polydor Pressing Operations plant. The disc contained a recording of Richard Strauss's Eine Alpensinfonie (in English, An Alpine Symphony), played by the Berlin Philharmonic and conducted by Herbert von Karajan. The first public demonstration was on the BBC television program Tomorrow's World when The Bee Gees' album Living Eyes (1981) was played. In August 1982 the real pressing was ready to begin in the new factory, not far from the place where Emil Berliner had produced his first gramophone record 93 years earlier. By now, Deutsche Grammophon, Berliner's company and the publisher of the Strauss recording, had become a part of PolyGram. The first CD to be manufactured at the new factory was The Visitors (1981) by ABBA. The first album to be released on CD was Billy Joel's 52nd Street, that reached the market alongside Sony's CD player CDP-101 on October 1, 1982 in Japan. Early the following year on March 2, 1983 CD players and discs (16 titles from CBS Records) were released in the United States and other markets. 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, the CD began to gain popularity in the larger popular and rock music markets. The first artist to sell a million copies on CD was Dire Straits, with its 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. In 1988, 400 million CDs were manufactured by 50 pressing plants around the world.
The CD was planned to be the successor of the gramophone 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 June 1985, the computer readable CD-ROM (read-only memory) and, in 1990, CD-Recordable were introduced, also developed by both Sony and Philips. The CD's compact format has largely replaced the audio cassette player in new automobile applications, and recordable CDs are an 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 have used the same form factor as CDs, and video players can usually play audio CDs as well. With the advent of the MP3 in the 2000s, the sales of CDs has dropped in seven out of the last eight years. In 2008, large label CD sales dropped 20%, although independent and DIY music sales may be tracking better according to figures released March 30, 2009.
A CD is made from 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 are stored as a series of 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.
Scanning velocity is 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 down during playback.)
The program area is 86.05 cm² and the length of the recordable spiral is (86.05 cm2 / 1.6 µm) = 5.38 km. With a scanning speed of 1.2 m/s, the playing time is 74 minutes, or 650 MB of data on a CD-ROM. A disc with data packed slightly more densely is tolerated by most players (though some old ones fail). Using a linear velocity of 1.2 m/s and a track pitch of 1.5 µm yields a playing time of 80 minutes, or a data capacity of 700 MB. Even higher capacities on non-standard discs (up to 99 minutes) are available at least as recordables, but generally the tighter the tracks are squeezed, the worse the compatibility.
A CD is read by focusing a 780 nm wavelength (near infrared) semiconductor laser 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.
The pits and lands themselves do not directly represent the zeros and ones of binary data. Instead, non-return-to-zero, inverted encoding is used: a change from pit to land or land to pit indicates a one, while no change indicates a series of zeros. There must be at least two and no more than ten zeros between each one, which is defined by the length of the pit. This in turn is decoded by reversing the eight-to-fourteen modulation used in mastering the disc, and then reversing the Cross-Interleaved Reed-Solomon Coding, finally revealing the raw data stored on the disc.
CDs are susceptible to damage from both normal use and 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 disk. Scratches on the clear side can be repaired by refilling them with similar refractive plastic, or by careful polishing.
The additional 14-minute playing time subsequently required changing to a 120 mm disc. Kees Immink, Philips' chief engineer, however, denies this, claiming that the increase was motivated by technical considerations, and that even after the increase in size, the Furtwängler recording would not have fit on one of the earliest CDs. the story is slightly more involved. In 1979, Philips owned PolyGram, one of the world's largest distributors of music. PolyGram had set up a large experimental CD plant in Hannover, Germany, which could produce huge numbers of CDs having, of course, a diameter of 115 mm. Sony did not yet have such a facility. If Sony had agreed on the 115-mm disc, Philips would have had a significant competitive edge in the market. Sony decided that something had to be done. The long playing time of Beethoven's Ninth Symphony imposed by Ohga was used to push Philips to accept 120 mm, so that Philips' PolyGram lost its edge on disc fabrication. typical of long-playing (LP) vinyl albums, was often used to the CD's advantage during the early years when CDs and LPs vied for commercial sales. CDs would often be released with one or more bonus tracks, enticing consumers to buy the CD for the extra material. However, attempts to combine double LPs onto one CD occasionally resulted in the opposite situation in which the CD would actually offer fewer tracks than the equivalent LP.
Playing times beyond 74 minutes are achieved by decreasing track pitch beyond the original red book standard. Most players can accommodate the more closely spaced data. Christian Thielemann's live Deutsche Grammophon recording of Bruckner's Fifth with the Munich Philharmonic in 2004 clocks at 82:34. The Kirov Orchestra recording of Pyotr Ilyich Tchaikovsky's The Nutcracker conducted by Valery Gergiev and released by Philips/PolyGram Records (catalogue number 462 114) on October 20, 1998, clocks at 81:14. Disc two of Gold (Deutche Grammophon/Universal Classics 477 743) by Herbert von Karajan clocks in at 81:21. The Mission of Burma compilation album Mission of Burma, released in 1988 by Rykodisc, previously held the record at 80:08.
These 588-bit frames are in turn grouped into sectors. Each sector contains 98 frames, totaling 98 × 24 = 2352 bytes of music. The CD is played at a speed of 75 sectors per second, which results in 176,400 bytes per second. Divided by two channels and two bytes per sample, this results in a sample rate of 44,100 samples per second.
For CD-ROM data discs, the physical frame and sector sizes are the same. Since error concealment cannot be applied to non-audio data in case the CIRC error correction fails to recover the user data, a third layer of error correction is defined, reducing the payload to 2048 bytes per sector for the Mode-1 CD-ROM format. To increase the data-rate for Video CD, Mode-2 CD-ROM, the third layer has been omitted, increasing the payload to 2336 user-available bytes per sector, only 16 bytes (for synchronization and header data) less than available in Red-Book audio.
Titles in the SACD format can be issued as hybrid discs; these discs contain the SACD audio stream as well as a standard audio CD layer which is playable in standard CD players, thus making them backward compatible.
The VCD standard was created in 1993 by Sony, Philips, Matsushita, and JVC and is referred to as the White Book standard.
Overall picture quality is intended to be comparable to VHS video. Poorly compressed VCD video can sometimes be lower quality than VHS video, but VCD exhibits block artifacts rather than analog noise, and does not deteriorate further with each use, which may be preferable.
352x240 (or SIF) resolution was chosen because it is half the vertical, and half the horizontal resolution of NTSC video. 352x288 is similarly one quarter PAL/SECAM resolution. This approximates the (overall) resolution of an analog VHS tape, which, although it has double the number of (vertical) scan lines, has a much lower horizontal resolution.
SVCD has two-thirds the resolution of DVD, and over 2.7 times the resolution of VCD. One CD-R disc can hold up to 60 minutes of standard quality SVCD-format video. While no specific limit on SVCD video length is mandated by the specification, one must lower the video bit rate, and therefore quality, in order to accommodate very long videos. It is usually difficult to fit much more than 100 minutes of video onto one SVCD without incurring significant quality loss, and many hardware players are unable to play video with an instantaneous bit rate lower than 300 to 600 kilobits per second.
The primary data formats for Enhanced Compact Disc's are mixed mode (Yellow Book/Red Book), CD-i, hidden track, and multisession (Blue Book).
This method produces the clear plastic blank part of the disc. After a metallic reflecting layer (usually aluminum, 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.
CD-R recordings are designed to be permanent. Over time the dye's physical characteristics may change, however, causing read errors and data loss until the reading device cannot recover with error correction methods. The design life is from 20 to 100 years, depending on the quality of the discs, the quality of the writing drive, and storage conditions. However, testing has demonstrated such degradation of some discs in as little as 18 months under normal storage conditions. This failure is known as CD rot. CD-Rs follow the Orange Book standard.
Original CD-RW drives can only write to original ReWritable CDs. High Speed CD-RW drives can typically write to both original ReWritable CD discs and High Speed ReWritable CD discs. Both types of CD-RW discs can be read in most CD drives.
Higher speed CD-RW discs, Ultra Speed (16x to 24x write speed) and Ultra Speed+ (32x write speed), are now available.
Category:1982 introductions Category:Audio storage Category:Digital audio Category:High-end audio Category:Video storage Category:Dutch inventions Category:Japanese inventions
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