Compact Disc

Compact Disc

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Encyclopedia
The Compact Disc is an optical disc
Optical disc
In computing and optical disc recording technologies, an optical disc is a flat, usually circular disc which encodes binary data in the form of pits and lands on a special material on one of its flat surfaces...

 used to store digital data
Data (computing)
In computer science, data is information in a form suitable for use with a computer. Data is often distinguished from programs. A program is a sequence of instructions that detail a task for the computer to perform...

. It was originally developed to store and playback sound recordings exclusively, but later expanded to encompass data storage (CD-ROM
CD-ROM
A CD-ROM is a pre-pressed compact disc that contains data accessible to, but not writable by, a computer for data storage and music playback. The 1985 “Yellow Book” standard developed by Sony and Philips adapted the format to hold any form of binary data....

), write-once audio and data storage (CD-R
CD-R
A CD-R is a variation of the Compact Disc invented by Philips and Sony. CD-R is a Write Once Read Many optical medium, though the whole disk does not have to be entirely written in the same session....

), rewritable media (CD-RW
CD-RW
A CD-RW is a rewritable optical disc. It was introduced in 1997, and was known as "CD-Writable" during development. It was preceded by the CD-MO, which was never commercially released....

), Video Compact Discs (VCD
VCD
VCD is a three-letter abbreviation with multiple meanings, as described below:* VCD Athletic, semi-professional football team* Video CD* Voice command device* Value change dump * Vocal cord dysfunction* Visual Communication and Design...

), Super Video Compact Discs (SVCD), PhotoCD, PictureCD, CD-i, and Enhanced CD. Audio CDs and audio CD players have been commercially available since October 1982.

Standard CDs have a diameter of 120 millimetres (4.7 in) and can hold up to 80 minutes of uncompressed audio or 700 MB
Megabyte
The megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...

 (700 × 220 bytes) of data. The Mini CD
Mini CD
Mini CDs, or “pocket CDs” are CDs with a smaller diameter and one third the capacity.-Formats:Amongst the various formats are the* Mini CD single, a small disc. The format is mainly used for audio CD singles in certain regions , much like the old vinyl single...

 has various diameters ranging from 60 to 80 mm (2.4 to 3.1 in); they are sometimes used for CD singles, storing up to 24 minutes of audio or delivering device driver
Device driver
In computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a hardware device....

s.

CD-ROMs and CD-Rs remain widely used technologies in the computer industry
Computer industry
Computer industry is a collective term used to describe the whole range of businesses involved in developing computer software, designing computer hardware and computer networking infrastructures, the manufacture of computer components and the provision of information technology services.-See...

. 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.

History



The Compact Disc is a spin-off of Laserdisc
Laserdisc
LaserDisc was a home video format and the first commercial optical disc storage medium. Initially licensed, sold, and marketed as MCA DiscoVision in North America in 1978, the technology was previously referred to interally as Optical Videodisc System, Reflective Optical Videodisc, Laser Optical...

 technology. Sony
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....

 first publicly demonstrated an optical digital audio disc in September 1976. In September 1978 they demonstrated an optical digital audio disc with a 150 minute playing time, and with specifications of 44,056 Hz sampling rate, 16-bit linear resolution, cross-interleaved
Cross-Interleaved Reed-Solomon Coding
In the compact disc system, cross-interleaved Reed-Solomon code provides error detection and error correction. CIRC adds to every three data bytes one redundant parity byte.-Overview:...

 error correction code, that were similar to those of the Compact Disc introduced in 1982. Technical details of Sony's digital audio disc were presented during the 62nd AES
Audio Engineering Society
Established in 1948, the Audio Engineering Society draws its membership from amongst engineers, scientists, other individuals with an interest or involvement in the professional audio industry. The membership largely comprises engineers developing devices or products for audio, and persons working...

 Convention, held on March 13–16, 1979, in Brussels
Brussels
Brussels , officially the Brussels Region or Brussels-Capital Region , is the capital of Belgium and the de facto capital of the European Union...

. On March 8, 1979 Philips
Philips
Koninklijke Philips Electronics N.V. , more commonly known as Philips, is a multinational Dutch electronics company....

 publicly demonstrated a prototype of an optical digital audio disc at a press conference called "Philips Introduce Compact Disc" in Eindhoven, Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...

. On March 6, 2009, Philips received an IEEE Milestone with the following 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."

Sony executive Norio Ohga
Norio Ohga
, otherwise spelled Norio Oga, was the former president and chairman of Sony Corporation, credited with spurring the development of the compact disc as a commercially viable audio format.-Early career:...

, 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
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....

 and Philips Consumer Electronics
Philips Consumer Electronics
Philips Consumer Lifestyle is a part of Philips ; which is one of the largest electronics companies in the world. In 2005, its sales were € 30.4 billion and it employed 161,500 people in more than 60 countries. Other Philips divisions are: Philips Lighting, Philips Healthcare, Philips Domestic...

 (Philips) set up a joint task force of engineers to design a new digital audio disc. Led by Kees Schouhamer Immink and Toshitada Doi
Toshitada Doi
is a Japanese electrical engineer, who played a significant role in the digital audio revolution. He received a degree in electrical engineering from the Tokyo Institute of Technology in 1964, and a PhD from Tohoku University in 1972. He joined Sony Japan in 1964. He started the first digital audio...

, the research pushed forward laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...

 and optical disc
Optical disc
In computing and optical disc recording technologies, an optical disc is a flat, usually circular disc which encodes binary data in the form of pits and lands on a special material on one of its flat surfaces...

 technology that began independently by Philips and Sony in 1977 and 1975, respectively. After a year of experimentation and discussion, the taskforce produced the Red Book
Red Book (audio CD standard)
Red Book is the standard for audio CDs . It is named after one of the Rainbow Books, a series of books that contain the technical specifications for all CD and CD-ROM formats.The first edition of the Red Book was released in 1980 by Philips and Sony; it was adopted by the Digital Audio Disc...

, the Compact Disc standard. Philips contributed the general manufacturing
Manufacturing
Manufacturing is the use of machines, tools and labor to produce goods for use or sale. The term may refer to a range of human activity, from handicraft to high tech, but is most commonly applied to industrial production, in which raw materials are transformed into finished goods on a large scale...

 process
Industrial process
Industrial processes are procedures involving chemical or mechanical steps to aid in the manufacture of an item or items, usually carried out on a very large scale. Industrial processes are the key components of heavy industry....

, based on video Laserdisc
Laserdisc
LaserDisc was a home video format and the first commercial optical disc storage medium. Initially licensed, sold, and marketed as MCA DiscoVision in North America in 1978, the technology was previously referred to interally as Optical Videodisc System, Reflective Optical Videodisc, Laser Optical...

 technology. Philips also contributed eight-to-fourteen modulation
Eight-to-Fourteen Modulation
Eight-to-fourteen modulation is a data encoding technique – formally, a channel code – used by compact discs and pre-Hi-MD MiniDiscs. EFMPlus is a related code, used in DVDs and SACDs. EFM and EFMPlus were both invented by Kees A...

 (EFM), which offers both a long playing time and a certain resilience to defects such as scratches and fingerprints, while Sony contributed the error-correction method, CIRC
Cross-Interleaved Reed-Solomon Coding
In the compact disc system, cross-interleaved Reed-Solomon code provides error detection and error correction. CIRC adds to every three data bytes one redundant parity byte.-Overview:...

. The Compact Disc Story, 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
Langenhagen
Langenhagen is a town in the Hanover district of Lower Saxony, Germany.-International relations:Langenhagen is twinned with: - Joinville - - Economy :...

 near Hannover, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

, by the Polydor Pressing Operations plant. The disc contained a recording of Richard Strauss
Richard Strauss
Richard Georg Strauss was a leading German composer of the late Romantic and early modern eras. He is known for his operas, which include Der Rosenkavalier and Salome; his Lieder, especially his Four Last Songs; and his tone poems and orchestral works, such as Death and Transfiguration, Till...

's Eine Alpensinfonie (in English
English language
English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...

, An Alpine Symphony), played by the Berlin Philharmonic and conducted by Herbert von Karajan
Herbert von Karajan
Herbert von Karajan was an Austrian orchestra and opera conductor. To the wider world he was perhaps most famously associated with the Berlin Philharmonic, of which he was principal conductor for 35 years...

. The first public demonstration was on the BBC
BBC
The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...

 television program Tomorrow's World
Tomorrow's World
Tomorrow's World was a long-running BBC television series, showcasing new developments in the world of science and technology. First aired on 7 July 1965 on BBC1, it ran for 38 years until it was cancelled at the beginning of 2003.- Content :...

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
The Visitors (ABBA album)
The Visitors is the eighth and final studio album by Swedish pop group ABBA, released on November 30, 1981.With The Visitors, ABBA took several steps away from the "lighter" pop music they had recorded previously and the album is often regarded as a more complex and mature effort...

(1981) by ABBA
ABBA
ABBA was a Swedish pop group formed in Stockholm in 1970 which consisted of Anni-Frid Lyngstad, Björn Ulvaeus, Benny Andersson and Agnetha Fältskog...

. The first album to be released on CD was Billy Joel's
Billy Joel
William Martin "Billy" Joel is an American musician and pianist, singer-songwriter, and classical composer. Since releasing his first hit song, "Piano Man", in 1973, Joel has become the sixth best-selling recording artist and the third best-selling solo artist in the United States, according to...

 52nd Street
52nd Street (album)
52nd Street is the sixth studio album by Billy Joel, released in 1978. It was also the first of many Joel albums to top the Billboard charts, along with his third and fourth Grammy win....

, that reached the market alongside Sony's CD player
Compact disc player
A Compact Disc player , or CD player, is an electronic device that plays audio Compact Discs. CD players are often a part of home stereo systems, car audio systems, and personal computers. They are also manufactured as portable devices...

 CDP-101
Sony CDP-101
The Sony CDP-101 was the world's first commercially released Compact Disc player. The system was launched in Japan on October 1, 1982 at a list price of 168,000 yen....

 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
Audiophile
An audiophile is a person who enjoys listening to recorded music, usually in a home. Some audiophiles are more interested in collecting and listening to music, while others are more interested in collecting and listening to audio components, whose "sound quality" they consider as important as the...

 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
Brothers in Arms (Dire Straits album)
- Original LP track listing :- 2005 Re-Issue 2 LP track listing :The 2005 Limited Edition Deluxe 180 gram High Performance Vinyl reissue contained the full-length versions of all songs by spreading out the songs over two half speed mastered LPs....

. The first major artist to have his entire catalogue converted to CD was David Bowie
David Bowie
David Bowie is an English musician, actor, record producer and arranger. A major figure for over four decades in the world of popular music, Bowie is widely regarded as an innovator, particularly for his work in the 1970s...

, whose 15 studio albums were made available by RCA Records
RCA Records
RCA Records is one of the flagship labels of Sony Music Entertainment. The RCA initials stand for Radio Corporation of America , which was the parent corporation from 1929 to 1985 and a partner from 1985 to 1986.RCA's Canadian unit is Sony's oldest label...

 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
Gramophone record
A gramophone record, commonly known as a phonograph record , vinyl record , or colloquially, a record, is an analog sound storage medium consisting of a flat disc with an inscribed, modulated spiral groove...

 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
CD-ROM
A CD-ROM is a pre-pressed compact disc that contains data accessible to, but not writable by, a computer for data storage and music playback. The 1985 “Yellow Book” standard developed by Sony and Philips adapted the format to hold any form of binary data....

 (read-only memory) and, in 1990, CD-R
CD-R
A CD-R is a variation of the Compact Disc invented by Philips and Sony. CD-R is a Write Once Read Many optical medium, though the whole disk does not have to be entirely written in the same session....

ecordable were introduced, also developed by both Sony and Philips. The CD's compact format has largely replaced the audio cassette
Compact Cassette
The Compact Cassette, often referred to as audio cassette, cassette tape, cassette, or simply tape, is a magnetic tape sound recording format. It was designed originally for dictation, but improvements in fidelity led the Compact Cassette to supplant the Stereo 8-track cartridge and reel-to-reel...

 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
MP3
MPEG-1 or MPEG-2 Audio Layer III, more commonly referred to as MP3, is a patented digital audio encoding format using a form of lossy data compression...

 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.

Physical details



A CD is made from 1.2 millimetre (0.047244094488189 in) thick, polycarbonate
Polycarbonate
PolycarbonatePhysical PropertiesDensity 1.20–1.22 g/cm3Abbe number 34.0Refractive index 1.584–1.586FlammabilityV0-V2Limiting oxygen index25–27%Water absorption – Equilibrium0.16–0.35%Water absorption – over 24 hours0.1%...

 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
Offset printing
Offset printing is a commonly used printing technique in which the inked image is transferred from a plate to a rubber blanket, then to the printing surface...

.

CD data is 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
Nanometre
A nanometre is a unit of length in the metric system, equal to one billionth of a metre. The name combines the SI prefix nano- with the parent unit name metre .The nanometre is often used to express dimensions on the atomic scale: the diameter...

 deep by 500 nm wide, and varies from 850 nm to 3.5 µm
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is 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
Constant linear velocity
In optical storage, constant linear velocity is a qualifier for the rated speed of an optical disc drive, and may also be applied to the writing speed of recordable discs. CLV implies that the angular velocity varies during an operation, as contrasted with CAV modes...

) – 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
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...

 (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
Photodiode
A photodiode is a type of photodetector capable of converting light into either current or voltage, depending upon the mode of operation.The common, traditional solar cell used to generateelectric solar power is a large area 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
Eight-to-Fourteen Modulation
Eight-to-fourteen modulation is a data encoding technique – formally, a channel code – used by compact discs and pre-Hi-MD MiniDiscs. EFMPlus is a related code, used in DVDs and SACDs. EFM and EFMPlus were both invented by Kees A...

 used in mastering the disc, and then reversing the Cross-Interleaved Reed-Solomon Coding
Cross-Interleaved Reed-Solomon Coding
In the compact disc system, cross-interleaved Reed-Solomon code provides error detection and error correction. CIRC adds to every three data bytes one redundant parity byte.-Overview:...

, 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.

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 MB data capacity. This capacity was reportedly specified by Sony executive Norio Ohga
Norio Ohga
, otherwise spelled Norio Oga, was the former president and chairman of Sony Corporation, credited with spurring the development of the compact disc as a commercially viable audio format.-Early career:...

 so as to be able to contain the entirety of Beethoven's Ninth Symphony on one disc. This diameter has been adopted by subsequent formats, including Super Audio CD
Super Audio CD
Super Audio CD is a high-resolution, read-only optical disc for audio storage. Sony and Philips Electronics jointly developed the technology, and publicized it in 1999. It is designated as the Scarlet Book standard. Sony and Philips previously collaborated to define the Compact Disc standard...

, DVD
DVD
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....

, HD DVD
HD DVD
HD DVD is a discontinued high-density optical disc format for storing data and high-definition video.Supported principally by Toshiba, HD DVD was envisioned to be the successor to the standard DVD format...

, and Blu-ray Disc
Blu-ray Disc
Blu-ray Disc is an optical disc storage medium designed to supersede the DVD format. The plastic disc is 120 mm in diameter and 1.2 mm thick, the same size as DVDs and CDs. Blu-ray Discs contain 25 GB per layer, with dual layer discs being the norm for feature-length video discs...

. 80 mm discs ("Mini CD
Mini CD
Mini CDs, or “pocket CDs” are CDs with a smaller diameter and one third the capacity.-Formats:Amongst the various formats are the* Mini CD single, a small disc. The format is mainly used for audio CD singles in certain regions , much like the old vinyl single...

s") were originally designed for CD singles
Single (music)
In music, a single or record single is a type of release, typically a recording of fewer tracks than an LP or a CD. This can be released for sale to the public in a variety of different formats. In most cases, the single is a song that is released separately from an album, but it can still appear...

 and can hold up to 24 minutes of music or 210 MB of data but never became popular. Today, nearly every single is released on a 120 mm CD, called a Maxi single
Maxi single
A maxi single or maxi-single is a music single release with more than the usual two tracks of an a-side song and a b-side song.-The first maxi singles:...

.

Novelty CDs are also available in numerous shapes and sizes, and are used chiefly for marketing. A common variant is the "business card" CD, a single with portions removed at the top and bottom making the disk resemble a business card.
Physical size Audio Capacity CD-ROM Data Capacity Note
120 mm 74–99 min 650–870 MB
Megabyte
The megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...

 
Standard size
80 mm 21–24 min 185–210 MB Mini-CD size
85x54 mm - 86x64 mm ~6 min 10-65 MB "Business card" size

Audio CD



The logical format of an audio CD (officially Compact Disc Digital Audio or CD-DA) is described in a document produced by the format's joint creators, Sony and Philips in 1980. The document is known colloquially as the "Red Book
Red Book (audio CD standard)
Red Book is the standard for audio CDs . It is named after one of the Rainbow Books, a series of books that contain the technical specifications for all CD and CD-ROM formats.The first edition of the Red Book was released in 1980 by Philips and Sony; it was adopted by the Digital Audio Disc...

" after the color of its cover. The format is a two-channel 16-bit PCM
Pulse-code modulation
Pulse-code modulation is a method used to digitally represent sampled analog signals. It is the standard form for digital audio in computers and various Blu-ray, Compact Disc and DVD formats, as well as other uses such as digital telephone systems...

 encoding at a 44.1 kHz sampling rate
Sampling rate
The sampling rate, sample rate, or sampling frequency defines the number of samples per unit of time taken from a continuous signal to make a discrete signal. For time-domain signals, the unit for sampling rate is hertz , sometimes noted as Sa/s...

 per channel. Four-channel sound
Four-channel compact disc digital audio
Compact Disc recordings contain two channels of 44.1-kHz 16-bit linear PCM audio. However, creators of the CD originally contemplated a four-channel, or quadraphonic, mode as well....

 is an allowable option within the Red Book format, but has never been implemented. Monaural
Monaural
Monaural or monophonic sound reproduction is single-channel. Typically there is only one microphone, one loudspeaker, or channels are fed from a common signal path...

 audio has no existing standard on a Red Book CD; mono-source material is usually presented as two identical channels on a 'stereo' track.

44.1 kHz sample rate



The selection of the sample rate was based primarily on the need to reproduce the audible frequency range of 20 Hz – 20 kHz. The Nyquist–Shannon sampling theorem
Nyquist–Shannon sampling theorem
The Nyquist–Shannon sampling theorem, after Harry Nyquist and Claude Shannon, is a fundamental result in the field of information theory, in particular telecommunications and signal processing. Sampling is the process of converting a signal into a numeric sequence...

 states that a sampling rate of more than twice the maximum frequency of the signal to be recorded is needed, resulting in a required rate of at least 40 kHz. The exact sampling rate of 44.1 kHz was inherited from a method of converting digital audio into an analog video signal for storage on U-matic video tape
U-matic
U-matic is an analog recording videocassette format first shown by Sony in prototype in October 1969, and introduced to the market in September 1971. It was among the first video formats to contain the videotape inside a cassette, as opposed to the various Reel-to-Reel or open-reel formats of the...

, which was the most affordable way to transfer data from the recording studio to the CD manufacturer at the time the CD specification was being developed. The device that converts an analog audio signal into PCM audio, which in turn is changed into an analog video signal is called a PCM adaptor
PCM adaptor
A PCM adaptor is a device used for recording digital audio in the PCM format, which in turn connects to a video cassette recorder for storage and playback of the digital audio information.-How a PCM adaptor works:...

. This technology could store six samples (three samples per stereo channel) in a single horizontal line. A standard NTSC
NTSC
NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...

 video signal has 245 usable lines per field, and 59.94 fields/s, which works out to be 44,056 samples/s/stereo channel. Similarly, PAL
PAL
PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...

 has 294 lines and 50 fields, which gives 44,100 samples/s/stereo channel. This system could store 14-bit samples with some error correction, or 16-bit samples with almost no error correction.

There was a long debate over the use of 14-bit (Philips) or 16-bit (Sony) quantization
Quantization (sound processing)
In signal processing and digital audio, quantization is the process of approximating a continuous range of values by a relatively small set of discrete symbols or integer values...

, and 44,056 or 44,100 samples/s (Sony) or approximately 44,000 samples/s (Philips). When the Sony/Philips task force designed the Compact Disc, Philips had already developed a 14-bit D/A converter
Digital-to-analog converter
In electronics, a digital-to-analog converter is a device that converts a digital code to an analog signal . An analog-to-digital converter performs the reverse operation...

, but Sony insisted on 16-bit. In the end, 16 bits and 44.1 kilosamples per second prevailed. Philips found a way to produce 16-bit quality using its 14-bit DAC by using four times oversampling
Oversampling
In signal processing, oversampling is the process of sampling a signal with a sampling frequency significantly higher than twice the bandwidth or highest frequency of the signal being sampled...

.

Storage capacity and playing time


The partners aimed at a playing time of 60 minutes with a disc diameter of 100 mm (Sony) or 115 mm (Philips). Sony vice-president Norio Ohga
Norio Ohga
, otherwise spelled Norio Oga, was the former president and chairman of Sony Corporation, credited with spurring the development of the compact disc as a commercially viable audio format.-Early career:...

 suggested extending the capacity to 74 minutes to accommodate Wilhelm Furtwängler
Wilhelm Furtwängler
Wilhelm Furtwängler was a German conductor and composer. He is widely considered to have been one of the greatest symphonic and operatic conductors of the 20th century. By the 1930s he had built a reputation as one of the leading conductors in Europe, and he was the leading conductor who remained...

's recording of Ludwig van Beethoven
Ludwig van Beethoven
Ludwig van Beethoven was a German composer and pianist. A crucial figure in the transition between the Classical and Romantic eras in Western art music, he remains one of the most famous and influential composers of all time.Born in Bonn, then the capital of the Electorate of Cologne and part of...

's Symphony No. 9
Symphony No. 9 (Beethoven)
The Symphony No. 9 in D minor, Op. 125, is the final complete symphony of Ludwig van Beethoven. Completed in 1824, the symphony is one of the best known works of the Western classical repertoire, and has been adapted for use as the European Anthem...

 from the 1951 Bayreuth Festival
Bayreuth Festival
The Bayreuth Festival is a music festival held annually in Bayreuth, Germany, at which performances of operas by the 19th century German composer Richard Wagner are presented...

.

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. According to a Sunday Tribune
Sunday Tribune
The Sunday Tribune was an Irish Sunday broadsheet newspaper published by Tribune Newspapers plc. It was edited in its final years by Nóirín Hegarty, who changed both the tone and the physical format of the newspaper from broadsheet to tabloid. Former editors include Conor Brady, Vincent Browne,...

interview, the story is slightly more involved. In 1979, Philips owned PolyGram
PolyGram
PolyGram was the name of the major label recording company started by Philips from as a holding company for its music interests in 1945. In 1999 it was sold to Seagram and merged into Universal Music Group.-Hollandsche Decca Distributie , 1929-1950:...

, 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
Norio Ohga
, otherwise spelled Norio Oga, was the former president and chairman of Sony Corporation, credited with spurring the development of the compact disc as a commercially viable audio format.-Early career:...

 was used to push Philips to accept 120 mm, so that Philips' PolyGram lost its edge on disc fabrication.

The 74-minute playing time of a CD, which was longer than the 20 minutes per side 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
Christian Thielemann
-Career:Thielemann studied viola and piano at the Hochschule für Musik in Berlin and took private lessons in composition and conducting before becoming répétiteur aged 19 at the Deutsche Oper Berlin with Heinrich Hollreiser and working as Herbert von Karajan's assistant...

's live Deutsche Grammophon
Deutsche Grammophon
Deutsche Grammophon is a German classical record label which was the foundation of the future corporation to be known as PolyGram. It is now part of Universal Music Group since its acquisition and absorption of PolyGram in 1999, and it is also UMG's oldest active label...

 recording of Bruckner's
Anton Bruckner
Anton Bruckner was an Austrian composer known for his symphonies, masses, and motets. The first are considered emblematic of the final stage of Austro-German Romanticism because of their rich harmonic language, complex polyphony, and considerable length...

 Fifth
Symphony No. 5 (Bruckner)
The Symphony No. 5 in B flat major of Anton Bruckner was written in 1875–1876, with a few minor changes over the next few years. It was first performed in public on two pianos by Joseph Schalk and Franz Zottmann on 20 April 1887 at the Bösendorfersaal in Vienna...

 with the Munich Philharmonic in 2004 clocks at 82:34. The Kirov Orchestra recording of Pyotr Ilyich Tchaikovsky
Pyotr Ilyich Tchaikovsky
Pyotr Ilyich Tchaikovsky Pyotr Ilyich Tchaikovsky Pyotr Ilyich Tchaikovsky (Russian: Пётр Ильи́ч Чайко́вский ; often "Peter Ilich Tchaikovsky" in English. His names are also transliterated "Piotr" or "Petr"; "Ilitsch", "Il'ich" or "Illyich"; and "Tschaikowski", "Tschaikowsky", "Chajkovskij"...

's The Nutcracker conducted by Valery Gergiev
Valery Gergiev
Valery Abisalovich Gergiev is a Russian conductor and opera company director. He is general director and artistic director of the Mariinsky Theatre, principal conductor of the London Symphony Orchestra, and artistic director of the White Nights Festival in St. Petersburg.- Early life :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
Herbert von Karajan
Herbert von Karajan was an Austrian orchestra and opera conductor. To the wider world he was perhaps most famously associated with the Berlin Philharmonic, of which he was principal conductor for 35 years...

 clocks in at 81:21. The Mission of Burma
Mission of Burma
Mission of Burma is an American post-punk band formed in Boston, Massachusetts in 1979. The band was formed by Roger Miller , Clint Conley , Peter Prescott and Martin Swope...

 compilation album Mission of Burma, released in 1988 by Rykodisc
Rykodisc
Rykodisc Records is an American record label. It is owned by Warner Music Group, operates as a unit of WMG's Independent Label Group and is distributed through Alternative Distribution Alliance.-Company history:...

, previously held the record at 80:08.

Data structure


The smallest entity in a CD is called a frame, which consists of 33 bytes and contains six complete 16-bit stereo samples (two bytes × two channels × six samples = 24 bytes). The other nine bytes consist of eight CIRC error-correction bytes and one subcode
Compact disc subcode
Besides digital audio, a compact disc contains digital data called subcode or subchannel data, which is multiplexed with the digital audio. The data in a CD are arranged in frames. A frame comprises 33 bytes, of which 24 bytes are audio , eight bytes are error correction , and one byte is for subcode...

 byte, used for control and display. Each byte is translated into a 14-bit word using eight-to-fourteen modulation, which alternates with three-bit merging words. In total there are 33 × (14 + 3) = 561 bits. A 27-bit unique synchronization word is added, so that the number of bits in a frame totals 588 (which are decoded to only 192 bits music).

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
Video CD
Before the advent of DVD and Blu-ray, the Video CD became the first format for distributing films on standard 120 mm optical discs. The format is a standard digital format for storing video on a Compact Disc...

, 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.
"Frame"

For the Red Book stereo audio CD, the time format is commonly measured in minutes, seconds and frames (mm:ss:ff), where one frame corresponds to one sector, or 1/75th of a second of stereo sound. In this context, the term frame is erroneously applied in editing applications and does not denote the physical frame described above. In editing and extracting, the frame is the smallest addressable time interval for an audio CD, meaning that track start and end positions can only be defined in 1/75 second steps.
Logical structure

The largest entity on a CD is called a track. A CD can contain up to 99 tracks (including a data track for mixed mode discs). Each track can in turn have up to 100 indexes, though players which handle this feature are rarely found outside of pro audio, particularly radio broadcasting. The vast majority of songs are recorded under index 1, with the pre-gap being index 0. Sometimes hidden track
Hidden track
In the field of recorded music, a hidden track is a piece of music that has been placed on a CD, audio cassette, vinyl record or other recorded medium in such a way as to avoid detection by the casual listener...

s are placed at the end of the last track of the disc, often using index 2 or 3. This is also the case with some discs offering "101 sound effects", with 100 and 101 being indexed as two and three on track 99. The index, if used, is occasionally put on the track listing as a decimal part of the track number, such as 99.2 or 99.3. (Information Society
Information Society (band)
Information Society is an American band originally from Minneapolis, Minnesota, primarily consisting of Kurt Larson , Paul Robb, and James Cassidy; the latter two reconvened the band in 2006, initially with Christopher Anton as lead vocalist, then with Harland rejoining them as lead vocalist by...

's Hack
Hack (album)
Hack is an album by freestyle synth-pop band Information Society. The album sold quite well but did not outsell its smash debut album. It is the only major-label-distributed title that has the modern Tommy Boy Records logo on it.-Track listing:...

was one of very few CD releases to do this, following a release with an equally obscure CD+G feature.) The track and index structure of the CD carried forward to the DVD as title and chapter, respectively.
Manufacturing tolerances

Current manufacturing processes allow an audio CD to contain up to 80 minutes (variable from one replication plant to another) without requiring the content creator to sign a waiver releasing the plant owner from responsibility if the CD produced is marginally or entirely unreadable by some playback equipment. Thus, in current practice, maximum CD playing time has crept higher by reducing minimum engineering tolerances; by and large, this has not unacceptably reduced reliability.

CD-Text



CD-Text is an extension of the Red Book specification for audio CD that allows for storage of additional text information (e.g., album name, song name, artist) on a standards-compliant audio CD. The information is stored either in the lead-in area of the CD, where there is roughly five kilobytes of space available, or in the subcode
Compact disc subcode
Besides digital audio, a compact disc contains digital data called subcode or subchannel data, which is multiplexed with the digital audio. The data in a CD are arranged in frames. A frame comprises 33 bytes, of which 24 bytes are audio , eight bytes are error correction , and one byte is for subcode...

 channels R to W on the disc, which can store about 31 megabytes.

CD + Graphics



Compact Disc + Graphics (CD+G) is a special audio Compact Disc that contains graphics data in addition to the audio data on the disc. The disc can be played on a regular audio CD player, but when played on a special CD+G player, can output a graphics signal (typically, the CD+G player is hooked up to a television set or a computer monitor); these graphics are almost exclusively used to display lyrics on a television set for karaoke
Karaoke
is a form of interactive entertainment or video game in which amateur singers sing along with recorded music using a microphone and public address system. The music is typically a well-known pop song minus the lead vocal. Lyrics are usually displayed on a video screen, along with a moving symbol,...

 performers to sing along with. The CD+G format takes advantage of the channels R through W. These six bits store the graphics information.
CD + Extended Graphics


Compact Disc + Extended Graphics (CD+EG, also known as CD+XG) is an improved variant of the Compact Disc + Graphics (CD+G) format. Like CD+G, CD+EG utilizes basic CD-ROM features to display text and video information in addition to the music being played. This extra data is stored in subcode
Compact disc subcode
Besides digital audio, a compact disc contains digital data called subcode or subchannel data, which is multiplexed with the digital audio. The data in a CD are arranged in frames. A frame comprises 33 bytes, of which 24 bytes are audio , eight bytes are error correction , and one byte is for subcode...

 channels R-W. Very few, if any, CD+EG discs have been published.

Super Audio CD



Super Audio CD (SACD) is a high-resolution read-only optical
Optical disc
In computing and optical disc recording technologies, an optical disc is a flat, usually circular disc which encodes binary data in the form of pits and lands on a special material on one of its flat surfaces...

 audio disc format that was designed to provide higher fidelity
High fidelity
High fidelity—or hi-fi—reproduction is a term used by home stereo listeners and home audio enthusiasts to refer to high-quality reproduction of sound or images, to distinguish it from the poorer quality sound produced by inexpensive audio equipment...

 digital audio reproduction than the Red Book. Introduced in 1999, it was developed by Sony and Philips, the same companies that created the Red Book. SACD was in a format war
Format war
A format war describes competition between mutually incompatible proprietary formats that compete for the same market, typically for data storage devices and recording formats for electronic media. It is often characterized by political and financial influence on content publishers by the...

 with DVD-Audio
DVD-Audio
DVD-Audio is a digital format for delivering high-fidelity audio content on a DVD. DVD-Audio is not intended to be a video delivery format and is not the same as video DVDs containing concert films or music videos....

, but neither has replaced audio CDs.

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
Backward compatibility
In the context of telecommunications and computing, a device or technology is said to be backward or downward compatible if it can work with input generated by an older device...

.

CD-MIDI


CD-MIDI
Musical Instrument Digital Interface
MIDI is an industry-standard protocol, first defined in 1982 by Gordon Hall, that enables electronic musical instruments , computers and other electronic equipment to communicate and synchronize with each other...

 is a format used to store music-performance data which upon playback is performed by electronic instruments that synthesize the audio. Hence, unlike Red Book, these recordings are not audio.

CD-ROM



For the first few years of its existence, the Compact Disc was a medium used purely for audio. However, in 1985 the Yellow Book CD-ROM standard was established by Sony and Philips, which defined a non-volatile optical data computer data storage
Computer storage
Computer data storage, often called storage or memory, refers to computer components and recording media that retain digital data. Data storage is one of the core functions and fundamental components of computers....

 medium using the same physical format as audio Compact Discs, readable by a computer with a CD-ROM drive.

Video CD (VCD)



Video CD (VCD, View CD, and Compact Disc digital video) is a standard digital
Digital
A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...

 format for storing video media on a CD. VCDs are playable in dedicated VCD players, most modern DVD-Video
DVD-Video
DVD-Video is a consumer video format used to store digital video on DVD discs, and is currently the dominant consumer video format in Asia, North America, Europe, and Australia. Discs using the DVD-Video specification require a DVD drive and a MPEG-2 decoder...

 players, personal computers, and some video game consoles.

The VCD standard was created in 1993 by Sony, Philips, Matsushita, and JVC
JVC
, usually referred to as JVC, is a Japanese international consumer and professional electronics corporation based in Yokohama, Japan which was founded in 1927...

 and is referred to as the White Book standard.

Overall picture quality is intended to be comparable to VHS
VHS
The Video Home System is a consumer-level analog recording videocassette standard developed by Victor Company of Japan ....

 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
Source Input Format
Source Input Format defined in MPEG-1, is a video format that was developed to allow the storage and transmission of digital video....

) 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.

Super Video CD



Super Video CD (Super Video Compact Disc or SVCD) is a format used for storing video media on standard Compact Discs. SVCD was intended as a successor to VCD and an alternative to DVD-Video, and falls somewhere between both in terms of technical capability and picture quality.

SVCD has two-thirds the resolution
Display resolution
The display resolution of a digital television or display device is the number of distinct pixels in each dimension that can be displayed. It can be an ambiguous term especially as the displayed resolution is controlled by all different factors in cathode ray tube , flat panel or projection...

 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.

Photo CD



Photo CD is a system designed by Kodak for digitizing and storing photos on a CD. Launched in 1992, the discs were designed to hold nearly 100 high quality images, scanned prints and slides using special proprietary encoding. Photo CDs are defined in the Beige Book
Rainbow Books
The Rainbow Books are a collection of standards defining the formats of Compact Discs.Red BookYellow BookThe Rainbow Books are a collection of standards defining the formats of Compact Discs.Red Book...

 and conform to the CD-ROM
CD-ROM
A CD-ROM is a pre-pressed compact disc that contains data accessible to, but not writable by, a computer for data storage and music playback. The 1985 “Yellow Book” standard developed by Sony and Philips adapted the format to hold any form of binary data....

 XA and CD-i Bridge specifications as well. They are intended to play on CD-i players, Photo CD players and any computer with the suitable software irrespective of the operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...

. The images can also be printed out on photographic paper with a special Kodak machine. This format is not to be confused with Kodak Picture CD
Picture CD
Picture CD is a product by Kodak, following on from the earlier Photo CD product. It holds photos from a single roll of color film, stored at 1024×1536 resolution using JPEG compression. The product is aimed at consumers...

, which is a consumer product in CD-ROM format.

CD-i



The Philips "Green Book" specifies the standard for interactive multimedia Compact Discs designed for CD-i
CD-i
CD-i, or Compact Disc Interactive, is the name of an interactive multimedia CD player developed and marketed by Royal Philips Electronics N.V. CD-i also refers to the multimedia Compact Disc standard used by the CD-i console, also known as Green Book, which was developed by Philips and Sony...

 players (1993). This format is unusual because it hides the initial tracks which contains the software and data files used by CD-i players by omitting the tracks from the disc's TOC (table of contents). This causes audio CD
Red Book (audio CD standard)
Red Book is the standard for audio CDs . It is named after one of the Rainbow Books, a series of books that contain the technical specifications for all CD and CD-ROM formats.The first edition of the Red Book was released in 1980 by Philips and Sony; it was adopted by the Digital Audio Disc...

 players to skip the CD-i data tracks. This is different from the CD-i Ready
CD-i Ready
CD-i Ready is a compact disc format based on the CD-i format. CD-i format and CD-i Ready format use different techniques to get audio CD players to skip over the CD-i software and data. CD-i Ready places the software and data in the pregap of Track 1. Standard CD-i format places the software and...

 format, which puts CD-i software and data into the pregap of track 1. CDi was the leading format of its time but was supplanted by the politics of competition. Philips Interactive Media lead the way in producing breakthrough titles, including the first interactive coloring book, Sesame Street Disc and children's programs, Groliers and Comptoms encyclopedias and many more pathbreaking programs.

Enhanced CD



Enhanced CD, also known as CD Extra and CD Plus, is a certification mark
Certification mark
A certification mark on a commercial product indicates five things:* The existence of a legal follow-up or product certification agreement between the manufacturer of a product and an organization with national accreditation for both testing and certification,* Legal evidence that the product was...

 of the Recording Industry Association of America
Recording Industry Association of America
The Recording Industry Association of America is a trade organization that represents the recording industry distributors in the United States...

 for various technologies that combine audio and computer data for use in both Compact Disc and CD-ROM
CD-ROM
A CD-ROM is a pre-pressed compact disc that contains data accessible to, but not writable by, a computer for data storage and music playback. The 1985 “Yellow Book” standard developed by Sony and Philips adapted the format to hold any form of binary data....

 players.

The primary data formats for Enhanced Compact Disc's are mixed mode
Mixed Mode CD
A Mixed Mode CD is a Compact Disc in which two different data types are combined. Typically the first track is a data track while the rest are audio tracks...

 (Yellow Book/Red Book
Red Book (audio CD standard)
Red Book is the standard for audio CDs . It is named after one of the Rainbow Books, a series of books that contain the technical specifications for all CD and CD-ROM formats.The first edition of the Red Book was released in 1980 by Philips and Sony; it was adopted by the Digital Audio Disc...

), CD-i
CD-i
CD-i, or Compact Disc Interactive, is the name of an interactive multimedia CD player developed and marketed by Royal Philips Electronics N.V. CD-i also refers to the multimedia Compact Disc standard used by the CD-i console, also known as Green Book, which was developed by Philips and Sony...

, hidden track, and multisession (Blue Book
Blue Book specification
The Blue Book or Enhanced Music CD specification describes the Enhanced Music CD format. The first session of an Enhanced Music CD contains audio information according to the Red Book...

).

VinylDisc



VinylDisc is the hybrid of a standard Audio CD and the vinyl record
Gramophone record
A gramophone record, commonly known as a phonograph record , vinyl record , or colloquially, a record, is an analog sound storage medium consisting of a flat disc with an inscribed, modulated spiral groove...

. The vinyl layer on the disc's label side can hold approximately three minutes of music.

Bootable CD



A bootable CD, or Live CD, is a CD that can be used to boot
Booting
In computing, booting is a process that begins when a user turns on a computer system and prepares the computer to perform its normal operations. On modern computers, this typically involves loading and starting an operating system. The boot sequence is the initial set of operations that the...

 a computer system. The CD can contain an operating system installer (e.g. Windows 2000, Windows XP), or even a full usable operating system, very common in the Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...

 world, with most distros
Linux distribution
A Linux distribution is a member of the family of Unix-like operating systems built on top of the Linux kernel. Such distributions are operating systems including a large collection of software applications such as word processors, spreadsheets, media players, and database applications...

, like Ubuntu
Ubuntu (operating system)
Ubuntu is a computer operating system based on the Debian Linux distribution and distributed as free and open source software. It is named after the Southern African philosophy of Ubuntu...

 or Fedora
Fedora (operating system)
Fedora is a RPM-based, general purpose collection of software, including an operating system based on the Linux kernel, developed by the community-supported Fedora Project and sponsored by Red Hat...

 offering fully usable Live CD
Live CD
A live CD, live DVD, or live disc is a CD or DVD containing a bootable computer operating system. Live CDs are unique in that they have the ability to run a complete, modern operating system on a computer lacking mutable secondary storage, such as a hard disk drive...

s.

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 2 to 3 seconds.

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.

Recordable CD




Recordable Compact Discs, CD-R
CD-R
A CD-R is a variation of the Compact Disc invented by Philips and Sony. CD-R is a Write Once Read Many optical medium, though the whole disk does not have to be entirely written in the same session....

s, are injection molded with a "blank" data spiral. A photosensitive dye is then applied, after which the discs are metalized and lacquer-coated. The write laser of the CD recorder changes the color of the dye to allow the read laser of a standard CD player to see the data, just as it would with a standard stamped disc. The resulting discs can be read by most CD-ROM drives and played in most audio CD players.

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 rot
Disc rot is a phrase describing the tendency of CD or DVD or other optical disks to become unreadable due to physical or chemical deterioration...

. CD-Rs follow the Orange Book
Rainbow Books
The Rainbow Books are a collection of standards defining the formats of Compact Discs.Red BookYellow BookThe Rainbow Books are a collection of standards defining the formats of Compact Discs.Red Book...

 standard.

Recordable audio CD


The recordable audio CD is designed to be used in a consumer audio CD recorder. These consumer audio CD recorders use SCMS (Serial Copy Management System
Serial Copy Management System
The Serial Copy Management System or SCMS is a copy protection scheme that was created in response to the digital audio tape invention, in order to prevent DAT recorders from making second-generation or serial copies. SCMS sets a "copy" bit in all copies, which prevents anyone from making further...

), an early form of digital rights management
Digital rights management
Digital rights management is a class of access control technologies that are used by hardware manufacturers, publishers, copyright holders and individuals with the intent to limit the use of digital content and devices after sale. DRM is any technology that inhibits uses of digital content that...

 (DRM), to conform to the AHRA (Audio Home Recording Act
Audio Home Recording Act
The Audio Home Recording Act of 1992 amended the United States copyright law by adding Chapter 10, "Digital Audio Recording Devices and Media"...

). The Recordable Audio CD is typically somewhat more expensive than CD-R due to (a) lower volume and (b) a 3% AHRA royalty used to compensate the music industry for the making of a copy.

High-capacity recordable CD


A higher density recording format that can hold:
  • 98.5 minutes of audio on a 12 cm disc (compared to about 80 minutes for Red Book audio).
  • 30 minutes of audio on an 8 cm disc (compared to about 24 minutes for Red Book audio).

ReWritable CD



CD-RW
CD-RW
A CD-RW is a rewritable optical disc. It was introduced in 1997, and was known as "CD-Writable" during development. It was preceded by the CD-MO, which was never commercially released....

 is a re-recordable medium that uses a metallic alloy instead of a dye. The write laser in this case is used to heat and alter the properties (amorphous vs. crystalline) of the alloy, and hence change its reflectivity. A CD-RW does not have as great a difference in reflectivity as a pressed CD or a CD-R, and so many earlier CD audio players cannot read CD-RW discs, although most later CD audio players and stand-alone DVD
DVD
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....

 players can. CD-RWs follow the Orange Book
Rainbow Books
The Rainbow Books are a collection of standards defining the formats of Compact Discs.Red BookYellow BookThe Rainbow Books are a collection of standards defining the formats of Compact Discs.Red Book...

 standard.

High-speed ReWritable CD


Due to technical limitations, the original ReWritable CD could be written no faster than 4x speed. High Speed ReWritable CD has a different design that permits writing at speeds ranging from 4x to 12x.

Original CD-RW drives can only write to original ReWritable CDs. High Speed CD-RW drives can typically write to both original ReWritable CDs and High Speed ReWritable CDs. 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.

ReWritable Audio CD


The ReWritable Audio CD is designed to be used in a consumer audio CD recorder, which won't (without modification) accept standard CD-RW discs. These consumer audio CD recorders use the Serial Copy Management System
Serial Copy Management System
The Serial Copy Management System or SCMS is a copy protection scheme that was created in response to the digital audio tape invention, in order to prevent DAT recorders from making second-generation or serial copies. SCMS sets a "copy" bit in all copies, which prevents anyone from making further...

 (SCMS), an early form of digital rights management
Digital rights management
Digital rights management is a class of access control technologies that are used by hardware manufacturers, publishers, copyright holders and individuals with the intent to limit the use of digital content and devices after sale. DRM is any technology that inhibits uses of digital content that...

 (DRM), to conform to the United States' Audio Home Recording Act
Audio Home Recording Act
The Audio Home Recording Act of 1992 amended the United States copyright law by adding Chapter 10, "Digital Audio Recording Devices and Media"...

 (AHRA). The ReWritable Audio CD is typically somewhat more expensive than CD-RW due to (a) lower volume and (b) a 3% AHRA royalty used to compensate the music industry for the making of a copy.

Copy protection



The Red Book audio specification, except for a simple 'anti-copy' bit in the subcode, does not include any copy protection
Copy protection
Copy protection, also known as content protection, copy obstruction, copy prevention and copy restriction, refer to techniques used for preventing the reproduction of software, films, music, and other media, usually for copyright reasons.- Terminology :Media corporations have always used the term...

 mechanism. Starting in early 2002, attempts were made by record companies to market "copy-protected" non-standard Compact Discs, which cannot be ripped, or copied, to hard drives or easily converted to MP3s. One major drawback to these copy-protected discs is that most will not play on either computer CD-ROM drives, or some standalone CD players that use CD-ROM mechanisms. Philips has stated that such discs are not permitted to bear the trademarked Compact Disc Digital Audio logo because they violate the Red Book specifications. Numerous copy-protection systems have been countered by readily available, often free, software.

See also


  • 5.1 Music Disc
    5.1 Music Disc
    The DTS Music Disc , DTS Audio CD or 5.1 Music Disc is an audio Compact Disc that contains music in surround sound format. It is a predecessor of DVD Audio. Physically, it conforms to the Red Book standard, except for the way the music is encoded on the CD...

  • Audio format
    Audio format
    An audio format is a medium for storing sound and music. The term is applied to both the physical recording media and the recording formats of the audio content – in computer science it is often limited to the audio file format, but its wider use usually refers to the physical method used to...

  • Audio storage
  • Bit rot
    Bit rot
    Bit rot, also known as bit decay, data rot, or data decay, is a colloquial computing term used to describe either a gradual decay of storage media or the degradation of a software program over time. The latter use of the term implies that software can wear out or rust like a physical tool...

  • Blu-ray disc
    Blu-ray Disc
    Blu-ray Disc is an optical disc storage medium designed to supersede the DVD format. The plastic disc is 120 mm in diameter and 1.2 mm thick, the same size as DVDs and CDs. Blu-ray Discs contain 25 GB per layer, with dual layer discs being the norm for feature-length video discs...

  • Compact-disc bronzing
  • Compact-disc player
    Compact disc player
    A Compact Disc player , or CD player, is an electronic device that plays audio Compact Discs. CD players are often a part of home stereo systems, car audio systems, and personal computers. They are also manufactured as portable devices...

  • Digipak
    Digipak
    Digipak is a patented style of CD, DVD or BD packaging, and is a registered trademark of AGI World Ltd., an Atlas Holdings company.-Features:...

  • Disk drive performance characteristics
  • DualDisc
    DualDisc
    DualDisc was a type of double-sided optical disc product developed by a group of record companies including EMI Music, Universal Music Group, Sony/BMG Music Entertainment, Warner Music Group, and 5.1 Entertainment Group and later under the aegis of the Recording Industry Association of America...

  • DVD
    DVD
    A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....

  • DVD-Audio
    DVD-Audio
    DVD-Audio is a digital format for delivering high-fidelity audio content on a DVD. DVD-Audio is not intended to be a video delivery format and is not the same as video DVDs containing concert films or music videos....

  • HD DVD
    HD DVD
    HD DVD is a discontinued high-density optical disc format for storing data and high-definition video.Supported principally by Toshiba, HD DVD was envisioned to be the successor to the standard DVD format...

  • High-Definition Compatible Digital
    High Definition Compatible Digital
    High Definition Compatible Digital, or HDCD is a patented encode-decode process, now owned by Microsoft, that improves the audio quality of standard Redbook audio CDs, while retaining backward compatibility with existing Compact disc players....

     (HDCD)
  • High fidelity
    High fidelity
    High fidelity—or hi-fi—reproduction is a term used by home stereo listeners and home audio enthusiasts to refer to high-quality reproduction of sound or images, to distinguish it from the poorer quality sound produced by inexpensive audio equipment...

  • Home cinema
    Home cinema
    Home cinema, also commonly called home theater, are home entertainment set-ups that seek to reproduce a movie theater experience and mood with the help of video and audio equipment in a private home....

  • Jewel case
  • K2 High Definition
    K2 High Definition
    K2 High Definition is a mastering technique developed by JVC Music. K2 HD encodes the music in 24 bit and 100 kHz resolution while in the mastering stage, even though the end product is a standard red book CD and does not require special hardware for playback.-External links: *...

  • Laserdisc
    Laserdisc
    LaserDisc was a home video format and the first commercial optical disc storage medium. Initially licensed, sold, and marketed as MCA DiscoVision in North America in 1978, the technology was previously referred to interally as Optical Videodisc System, Reflective Optical Videodisc, Laser Optical...

  • Longbox
    Longbox
    A longbox is a form of exterior paperboard packaging for musical compact discs in widespread use in the 1980s and early 1990s in North America.- Background :...

  • MildDisc
    MildDisc
    Sanyo Electric's subsidiary Sanyo Mavic Media has developed MildDisc which went to market in December 2003. The disc is based on polylactic acid which is produced from corn. It was planned to replace completely plastic compact discs, because it is recyclable and environmentally friendly...

  • MP3 CD
    MP3 CD
    An MP3 CD is a Compact Disc that contains digital audio in the MP3 file format. Discs are written in the Yellow Book standard data format , as opposed to the Red Book standard audio format ....

  • Rainbow Books
    Rainbow Books
    The Rainbow Books are a collection of standards defining the formats of Compact Discs.Red BookYellow BookThe Rainbow Books are a collection of standards defining the formats of Compact Discs.Red Book...

  • SPARS code
    SPARS Code
    SPARS is an acronym for the Society of Professional Audio Recording Services. The SPARS code is a three-letter code that appears on some Compact Disc recordings telling the consumer whether analog or digital equipment was used in producing the recording...

     explains AAD, ADD, DAD, and DDD
  • Video Single Disc
    Video Single Disc
    Video Single Disc was a disc-based format that carried the same analog video information as a laserdisc, but on a 12-centimetre diameter CD-DA-sized disc. It was a variation on the CD Video format, except VSD disc carried only video. It did not have any additional audio tracks like CD-V...

  • Virtual drive
    Virtual drive
    A virtual drive in computing is a device that to the operating system appears to be an ordinary physical disk drive, with disc images substituted for disc reading hardware through the use of software called a disk emulator...



Further reading


External links