Compact Disc Digital Audio (CDDA or CD-DA), also known as Digital Audio Compact Disc or simply as Audio CD, is the standard format for audio

compact disc The compact disc (CD) is a digital optical disc data storage format that was co-developed by Philips and Sony to store and play digital audio recordings. In August 1982, the first compact disc was manufactured. It was then released in Octo ...

s. The standard is defined in the ''Red Book'', one of a series of Rainbow Books (named for their binding colors) that contain the technical specifications for all CD formats. The first commercially available audio

CD player A CD player is an electronic device that plays audio compact discs, which are a digital optical disc data storage format. CD players were first sold to consumers in 1982. CDs typically contain recordings of audio material such as music or au ...

, the Sony CDP-101, was released October 1982 in Japan. The format gained worldwide acceptance in 1983–84, selling more than a million CD players in those two years, to play 22.5 million discs. Beginning in the 2000s, CDs were increasingly being replaced by other forms of digital storage and distribution, with the result that by 2010 the number of audio CDs being sold in the U.S. had dropped about 50% from their peak; however, they remained one of the primary distribution methods for the

music industry The music industry consists of the individuals and organizations that earn money by writing songs and musical compositions, creating and selling recorded music and sheet music, presenting concerts, as well as the organizations that aid, trai ...

. In the 2010s, revenues from digital music services, such as iTunes,

Spotify Spotify (; ) is a proprietary Swedish audio streaming and media services provider founded on 23 April 2006 by Daniel Ek and Martin Lorentzon. It is one of the largest music streaming service providers, with over 456 million monthly active us ...

, and YouTube, matched those from physical format sales for the first time. According to the

RIAA The Recording Industry Association of America (RIAA) is a trade organization that represents the music recording industry in the United States. Its members consist of record labels and distributors that the RIAA says "create, manufacture, and/ ...

's midyear report in 2020, phonograph record revenues surpassed those of CDs for the first time since the 1980s.

History

The optophone, first presented in 1931, was an early device which used light for both recording and playback of sound signals on a transparent photograph. More than thirty years later, American inventor

James T. Russell James is a common English language surname and given name: *James (name), the typically masculine first name James * James (surname), various people with the last name James James or James City may also refer to: People * King James (disambiguat ...

has been credited with inventing the first system to record digital video on an optical transparent foil that is lit from behind by a high-power halogen lamp, not a laser. Russell's patent application was filed in 1966, and he was granted a patent in 1970. Following litigation, Sony and Philips licensed Russell's patents for recording, not the play-back part (then held by a Canadian company, Optical Recording Corp.) in the 1980s. It is debatable whether Russell's concepts, patents, and prototypes instigated and in some measure influenced compact disc's design. The compact disc is an evolution of LaserDisc technology, where a focused

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The firs ...

beam is used that enables the high information density required for high-quality digital audio signals. Unlike the prior art by Optophonie and James Russell, the information on the disc is read from a reflective layer using a laser as a light source through a protective substrate. Prototypes were developed by

Philips Koninklijke Philips N.V. (), commonly shortened to Philips, is a Dutch multinational conglomerate corporation that was founded in Eindhoven in 1891. Since 1997, it has been mostly headquartered in Amsterdam, though the Benelux headquarters is ...

and

Sony , commonly stylized as SONY, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. As a major technology company, it operates as one of the world's largest manufacturers of consumer and professional ...

independently in the late 1970s. Although originally dismissed by

Philips Research The Philips Natuurkundig Laboratorium (English translation: ''Philips Physics Laboratory'') or NatLab was the Dutch section of the Philips research department, which did research for the product divisions of that company. Originally located in th ...

management as a trivial pursuit, the CD became the primary focus for Philips as the LaserDisc format struggled. In 1979, Sony and Philips set up a joint task force of engineers to design a new digital audio disc. After a year of experimentation and discussion, the '' Red Book'' CD-DA standard was published in 1980. After their commercial release in 1982, compact discs and their players were extremely popular. Despite costing up to $1,000, over 400,000 CD players were sold in the United States between 1983 and 1984. By 1988, CD sales in the United States surpassed those of vinyl LPs, and by 1992 CD sales surpassed those of prerecorded music cassette tapes. The success of the compact disc has been credited to the cooperation between

and

, which together agreed upon and developed compatible hardware. The unified design of the compact disc allowed consumers to purchase any disc or player from any company, and allowed the CD to dominate the at-home music market unchallenged.

Digital audio laser-disc prototypes

In 1974, Lou Ottens, director of the audio division of

, started a small group to develop an analog optical audio disc with a diameter of and a sound quality superior to that of the vinyl record. However, due to the unsatisfactory performance of the analog format, two Philips research engineers recommended a digital format in March 1974. In 1977, Philips then established a laboratory with the mission of creating a digital audio disc. The diameter of Philips's prototype compact disc was set at , the diagonal of an audio cassette.

Heitaro Nakajima was a Japanese digital audio pioneer, who led Sony's Compact Disc project in the 1970s. Born in Kurume, Fukuoka Prefecture, Nakajima graduated from the Tokyo Institute of Technology with a bachelor's degree in electrical engineering in 1944, an ...

, who developed an early digital audio recorder within Japan's national public broadcasting organization NHK in 1970, became general manager of

's audio department in 1971. His team developed a digital

PCM adaptor A PCM adaptor is a device that encodes digital audio as video for recording on a videocassette recorder. The adapter also has the ability to decode a video signal back to digital audio for playback. This digital audio system was used for mas ...

audio tape recorder using a

Betamax Betamax (also known as Beta, as in its logo) is a consumer-level analog recording and cassette format of magnetic tape for video, commonly known as a video cassette recorder. It was developed by Sony and was released in Japan on May 10, 197 ...

video recorder in 1973. After this, in 1974 the leap to storing digital audio on an optical disc was easily made.

first publicly demonstrated an optical digital audio disc in September 1976. A year later, in September 1977, Sony showed the press a disc that could play an hour of digital audio (44,100 Hz sampling rate and 16-bit resolution) using MFM modulation. In September 1978, the company demonstrated an optical digital audio disc with a 150-minute playing time, 44,056 Hz sampling rate, 16-bit linear resolution, and cross-interleaved

error correction In information theory and coding theory with applications in computer science and telecommunication, error detection and correction (EDAC) or error control are techniques that enable reliable delivery of digital data over unreliable communic ...

code—specifications similar to those later settled upon for the standard compact disc format in 1980. Technical details of Sony's digital audio disc were presented during the 62nd

AES AES may refer to: Businesses and organizations Companies * AES Corporation, an American electricity company * AES Data, former owner of Daisy Systems Holland * AES Eletropaulo, a former Brazilian electricity company * AES Andes, formerly AES Gener ...

Convention, held on 13–16 March 1979, in

Brussels Brussels (french: Bruxelles or ; nl, Brussel ), officially the Brussels-Capital Region (All text and all but one graphic show the English name as Brussels-Capital Region.) (french: link=no, Région de Bruxelles-Capitale; nl, link=no, Bruss ...

. Sony's AES technical paper was published on 1 March 1979. A week later, on 8 March, Philips publicly demonstrated a prototype of an optical digital audio disc at a press conference called "Philips Introduce Compact Disc" in

Eindhoven Eindhoven () is a city and municipality in the Netherlands, located in the southern province of North Brabant of which it is its largest. With a population of 238,326 on 1 January 2022, Sony executive

Norio Ohga , otherwise spelled ''Norio Oga'' (January 29, 1930 – April 23, 2011), was the former president and chairman of Sony Corporation, credited with spurring the development of the compact disc as a commercially viable audio format. Biography Early ...

, later CEO and chairman of Sony, and

were convinced of the format's commercial potential and pushed further development despite widespread skepticism.

Collaboration and standardization

In 1979, Sony and Philips set up a joint task force of engineers to design a new digital audio disc. Led by engineers

Kees Schouhamer Immink Kornelis Antonie "Kees" Schouhamer Immink (born 18 December 1946) is a Dutch scientist, inventor, and entrepreneur, who pioneered and advanced the era of digital audio, video, and data recording, including popular digital media such as Compact D ...

and

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 ...

, the research pushed forward

and

optical disc In computing and optical disc recording technologies, an optical disc (OD) is a flat, usually circular disc that encodes binary data (bits) in the form of pits and lands on a special material, often aluminum, on one of its flat surfaces. ...

technology. After a year of experimentation and discussion, the task force produced the '' Red Book'' CD-DA standard. First published in 1980, the standard was formally adopted by the IEC as an international standard in 1987, with various amendments becoming part of the standard in 1996. Philips coined the term ''compact disc'' in line with another audio product, the

Compact Cassette The Compact Cassette or Musicassette (MC), also commonly called the tape cassette, cassette tape, audio cassette, or simply tape or cassette, is an analog magnetic tape recording format for audio recording and playback. Invented by Lou Otten ...

, and contributed the general manufacturing

process A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management *Business process, activities that produce a specific se ...

, based on video LaserDisc technology. Philips also contributed

eight-to-fourteen modulation Eight-to-fourteen modulation (EFM) is a data encoding technique – formally, a ''line code'' – used by compact discs (CD), laserdiscs (LD) and pre- Hi-MD MiniDiscs. EFMPlus is a related code, used in DVDs and Super Audio CDs (SACDs). EFM an ...

(EFM), while Sony contributed the error-correction method, CIRC, which offers a certain resilience to defects such as scratches and fingerprints. The ''Compact Disc Story'', told by a former member of the task force, gives background information on the many technical decisions made, including the choice of the sampling frequency, playing time, and disc diameter. The task force consisted of around 6 persons, though according to Philips, the compact disc was "invented collectively by a large group of people working as a team."

Initial launch and adoption

Philips established the Polydor Pressing Operations plant in

Langenhagen Langenhagen ( Eastphalian: ''Langenhogen'') is a town in the Hanover district of Lower Saxony, Germany. History From 1866 to 1868 Robert Koch worked in Langenhagen. On June 18, 1972, Red Army Faction terrorist Ulrike Meinhof was arrested in L ...

near

Hannover Hanover (; german: Hannover ; nds, Hannober) is the capital and largest city of the German state of Lower Saxony. Its 535,932 (2021) inhabitants make it the 13th-largest city in Germany as well as the fourth-largest city in Northern Germany ...

, Germany, and quickly passed a series of milestones. * The first ''test pressing'' was of a recording of

Richard Strauss Richard Georg Strauss (; 11 June 1864 – 8 September 1949) was a German composer, conductor, pianist, and violinist. Considered a leading composer of the late Romantic music, Romantic and early Modernism (music), modern eras, he has been descr ...

's ''

Eine Alpensinfonie ''An Alpine Symphony'' (''Eine Alpensinfonie''), Op. 64, is a tone poem for large orchestra written by German composer Richard Strauss in 1915. It is one of Strauss's largest non-operatic works; the score calls for about 125 players and a t ...

'' (''An Alpine Symphony''), recorded December 1-3, 1980 and played by the

Berlin Philharmonic The Berlin Philharmonic (german: Berliner Philharmoniker, links=no, italic=no) is a German orchestra based in Berlin. It is one of the most popular, acclaimed and well-respected orchestras in the world. History The Berlin Philharmonic was fo ...

and conducted by

Herbert von Karajan Herbert von Karajan (; born Heribert Ritter von Karajan; 5 April 1908 – 16 July 1989) was an Austrian conductor. He was principal conductor of the Berlin Philharmonic for 34 years. During the Nazi era, he debuted at the Salzburg Festival, wi ...

, who had been enlisted as an ambassador for the format in 1979. * The first ''public demonstration'' was on the BBC television programme ''

Tomorrow's World ''Tomorrow's World'' is a former British television series about contemporary developments in science and technology. First transmitted on 7 July 1965 on BBC1, it ran for 38 years until it was cancelled at the beginning of 2003. The ''Tomorro ...

'' in 1981, when the

Bee Gees The Bee Gees were a musical group formed in 1958 by brothers Barry, Robin, and Maurice Gibb. The trio were especially successful in popular music in the late 1960s and early 1970s, and later as prominent performers in the disco music era i ...

' album '' Living Eyes'' (1981) was played. * The first ''commercial'' compact disc was produced on 17 August 1982, a 1979 recording of Chopin waltzes by

Claudio Arrau Claudio Arrau León (; February 6, 1903June 9, 1991) was a Chilean pianist known for his interpretations of a vast repertoire spanning the baroque to 20th-century composers, especially Bach, Beethoven, Schubert, Chopin, Schumann, Liszt and Br ...

. * The first 50 titles were ''released'' in Japan on 1 October 1982, the first of which was a re-release of the

Billy Joel William Martin Joel (born May 9, 1949) is an American singer, pianist and songwriter. Commonly nicknamed the " Piano Man" after his album and signature song of the same name, he has led a commercially successful career as a solo artist since th ...

album ''

52nd Street 52nd Street is a -long one-way street traveling west to east across Midtown Manhattan, New York City. A short section of it was known as the city's center of jazz performance from the 1930s to the 1950s. Jazz center Following the repeal of P ...

''. * The first CD played on BBC Radio was in October 1982 on BBC Radio Scotland ( Jimmy Mack programme, Followed by Ken Bruce and Eddie Mair all BBC Scotland), with the first CD ''played'' on UK independent radio station shortly after ( Radio Forth, Jay Crawford Show). The CD was the

Dire Straits Dire Straits were a British rock band formed in London in 1977 by Mark Knopfler (lead vocals and lead guitar), David Knopfler (rhythm guitar and backing vocals), John Illsley (bass guitar and backing vocals) and Pick Withers (drums and pe ...

album '' Love Over Gold''. The Japanese launch was followed on 14 March 1983 by the introduction of CD players and discs to Europe and North America (where CBS Records released sixteen titles). The growing acceptance of the CD in 1983 marks the beginning of the popular digital audio revolution. It was enthusiastically received, especially in the early-adopting classical music and

audiophile An audiophile is a person who is enthusiastic about high-fidelity sound reproduction. An audiophile seeks to reproduce the sound of a piece of recorded music or a live musical performance, typically inside closed headphones, In-ear monitors, open ...

communities, and its handling quality received particular praise. As the price of players gradually came down, and with the introduction of the portable

Discman Discman was Sony's brand name for portable CD players. The first Discman, the Sony D-50 or D-5 (depending on region), was launched in 1984. The brand name changed to CD Walkman, initially for Japanese lineups launched between October 1997 and Ma ...

, the CD began to gain popularity in the larger popular and rock music markets. With the rise in CD sales, pre-recorded cassette tape sales began to decline in the late 1980s; CD sales overtook cassette sales in the early 1990s. The first artist to sell a million copies on CD was

, with their 1985 album '' Brothers in Arms''.''

Maxim Maxim or Maksim may refer to: Entertainment *Maxim (magazine), ''Maxim'' (magazine), an international men's magazine ** Maxim (Australia), ''Maxim'' (Australia), the Australian edition ** Maxim (India), ''Maxim'' (India), the Indian edition *Maxim ...

'', 2004 One of the first CD markets was devoted to reissuing popular music whose commercial potential was already proven. The first major artist to have their entire catalog converted to CD was

David Bowie David Robert Jones (8 January 194710 January 2016), known professionally as David Bowie ( ), was an English singer-songwriter and actor. A leading figure in the music industry, he is regarded as one of the most influential musicians of the ...

, whose first fourteen studio albums of (then) sixteen were made available by

RCA Records RCA Records is an American record label currently owned by Sony Music Entertainment, a subsidiary of Sony Corporation of America. It is one of Sony Music's four flagship labels, alongside RCA's former long-time rival Columbia Records; also ...

in February 1985, along with four greatest hits albums; his fifteenth and sixteenth albums had already been issued on CD by

EMI Records EMI Records (formerly EMI Records Ltd.) is a multinational record label owned by Universal Music Group. It originally founded as a British flagship label by the music company of the same name in 1972, and launched in January 1973 as the succ ...

in 1983 and 1984, respectively.The New Schwann Record & Tape Guide Volume 37 No. 2 February 1985 On 26 February 1987, the first four UK albums by

the Beatles The Beatles were an English rock band, formed in Liverpool in 1960, that comprised John Lennon, Paul McCartney, George Harrison and Ringo Starr. They are regarded as the most influential band of all time and were integral to the developm ...

were released in mono on compact disc. In 1988, 400 million CDs were manufactured by 50 pressing plants around the world.MAC Audio News. No. 178, November 1989. pp 19–21 Glenn Baddeley. ''November 1989 News Update''. Melbourne Audio Club Inc.

Further development

Early CD players employed binary-weighted

digital-to-analog converter In electronics, a digital-to-analog converter (DAC, D/A, D2A, or D-to-A) is a system that converts a digital signal into an analog signal. An analog-to-digital converter (ADC) performs the reverse function. There are several DAC archi ...

s (DAC), which contained individual electrical components for each bit of the DAC. Even when using high-precision components, this approach was prone to decoding errors, exacerbated by the "zero-crossing problem". Another issue was

jitter In electronics and telecommunications, jitter is the deviation from true periodicity of a presumably periodic signal, often in relation to a reference clock signal. In clock recovery applications it is called timing jitter. Jitter is a significa ...

, not an amplitude- but a time-related defect. Confronted with the instability of DACs, manufacturers initially turned to increasing the number of bits in the DAC and using several DACs per audio channel, averaging their output. This increased the cost of CD players but did not solve the core problem. A breakthrough in the late 1980s culminated in development of "1-bit" DAC, which converts high-resolution low-frequency digital input signal into a lower-resolution high-frequency signal that is mapped to voltages and then smoothed with an analog filter. The temporary use of a lower-resolution signal simplified circuit design and improved efficiency, which is why it became dominant in CD players starting from the early 1990s. Philips used a variation of this technique called

pulse-density modulation Pulse-density modulation, or PDM, is a form of modulation used to represent an analog signal with a binary signal. In a PDM signal, specific amplitude values are not encoded into codewords of pulses of different weight as they would be in pulse-c ...

(PDM), while Matsushita (now

Panasonic formerly between 1935 and 2008 and the first incarnation of between 2008 and 2022, is a major Japanese multinational conglomerate corporation, headquartered in Kadoma, Osaka. It was founded by Kōnosuke Matsushita in 1918 as a lightbulb ...

) chose

pulse-width modulation Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a method of reducing the average power delivered by an electrical signal, by effectively chopping it up into discrete parts. The average value of voltage (and current) fed ...

(PWM), advertising it as "MASH", which is an acronym derived from their patented Multi-stAge noiSe-sHaping PWM topology. The CD was primarily planned as the successor to the

vinyl record A phonograph record (also known as a gramophone record, especially in British English), or simply a record, is an analog sound storage medium in the form of a flat disc with an inscribed, modulated spiral groove. The groove usually starts near ...

for playing music, rather than as a data storage medium. However, CDs have grown to encompass other applications. In 1983, following the CD's introduction, Immink and Joseph Braat presented the first experiments with erasable compact discs during the 73rd

Convention. In June 1985, the computer-readable CD-ROM (read-only memory) and, in 1990,

CD-R CD-R (Compact disc-recordable) is a digital optical disc storage format. A CD-R disc is a compact disc that can be written once and read arbitrarily many times. CD-R discs (CD-Rs) are readable by most CD readers manufactured prior to the int ...

ecordable were introduced.The world's first CD-R was made by the Japanese firm

Taiyo Yuden is a Japanese materials and electronics company, situated in Kyobashi, Chuo, Tokyo, that helped pioneer recordable CD technology (CD-R) along with Sony and Philips in 1988. Founded 70 years ago, Taiyo Yuden currently operates factories in Jap ...

Co., Ltd. in 1988 as part of the joint Philips-Sony development effort. Recordable CDs became an alternative to tape for recording and distributing music and could be duplicated without degradation in sound quality. Other newer video formats such as DVD and

Blu-ray The Blu-ray Disc (BD), often known simply as Blu-ray, is a digital optical disc data storage format. It was invented and developed in 2005 and released on June 20, 2006 worldwide. It is designed to supersede the DVD format, and capable of s ...

use the same physical geometry as CD, and most DVD and Blu-ray players are

backward compatible Backward compatibility (sometimes known as backwards compatibility) is a property of an operating system, product, or technology that allows for interoperability with an older legacy system, or with input designed for such a system, especially ...

with audio CD. CD sales in the United States peaked by 2000. By the early 2000s, the CD player had largely replaced the

audio cassette The Compact Cassette or Musicassette (MC), also commonly called the tape cassette, cassette tape, audio cassette, or simply tape or cassette, is an analog magnetic tape recording format for audio recording and playback. Invented by Lou Otten ...

player as standard equipment in new automobiles, with 2010 being the final model year for any car in the United States to have a factory-equipped cassette player.

Decline

With the advent and popularity of Internet-based distribution of files in lossy-compressed audio formats such as

MP3 MP3 (formally MPEG-1 Audio Layer III or MPEG-2 Audio Layer III) is a coding format for digital audio developed largely by the Fraunhofer Society in Germany, with support from other digital scientists in the United States and elsewhere. Orig ...

, sales of CDs began to decline in the 2000s. For example, between 2000 and 2008, despite overall growth in music sales and one anomalous year of increase, major-label CD sales declined overall by 20%, although independent and DIY music sales may be tracking better according to figures released 30 March 2009, and CDs still continue to sell greatly. As of 2012, CDs and DVDs made up only 34% of music sales in the United States. , only 24% of music in the United States was purchased on physical media, 2/3 of this consisting of CDs; however, in the same year in Japan, over 80% of music was bought on CDs and other physical formats. In 2018, U.S. CD sales were 52 million units—less than 6% of the peak sales volume in 2000. In the UK 32 million units were sold, almost 100 million fewer than in 2008. During the 2010s, the increasing popularity of solid-state media and music streaming services caused automakers to remove automotive CD players in favor of minijack auxiliary inputs, wired connections to USB devices and wireless

Bluetooth Bluetooth is a short-range wireless technology standard that is used for exchanging data between fixed and mobile devices over short distances and building personal area networks (PANs). In the most widely used mode, transmission power is limit ...

connections. Automakers viewed CD players as using up valuable space and taking up weight which could be reallocated to more popular features, like large touchscreens. By 2021, only

Lexus is the luxury vehicle division of the Japanese automaker Toyota. The Lexus brand is marketed in more than 90 countries and territories worldwide and is Japan's largest-selling make of premium cars. It has ranked among the 10 largest Japanese ...

and General Motors were still including CD players as standard equipment with certain vehicles. Despite rapidly declining sales year-over-year, the pervasiveness of the technology lingered for a time, with companies placing CDs in pharmacies, supermarkets, and filling station convenience stores to target buyers less likely to be able to use Internet-based distribution. In 2018

Best Buy Best Buy Co. Inc. is an American multinational consumer electronics retailer headquartered in Richfield, Minnesota. Originally founded by Richard M. Schulze and James Wheeler in 1966 as an audio specialty store called Sound of Music, it was rebra ...

announced plans to decrease their focus on CD sales, however, while continuing to sell records, sales of which are growing during the vinyl revival. CDs continued to be strong in some markets such as Japan where 132 million units were produced in 2019. The decline in CD sales has slowed in recent years, and in 2021 CD sales increased in the US for the first time since 2004, with Axios citing its rise to "young people who are finding they like hard copies of music in the digital age". It came at the same time as both physical vinyl and cassette reaching sales levels not seen in 30 years.

Awards and accolades

Sony and Philips received praise for the development of the compact disc from professional organizations. These awards include * Technical

Grammy Award The Grammy Awards (stylized as GRAMMY), or simply known as the Grammys, are awards presented by the Recording Academy of the United States to recognize "outstanding" achievements in the music industry. They are regarded by many as the most pre ...

for Sony and Philips, 1998. *

IEEE The Institute of Electrical and Electronics Engineers (IEEE) is a 501(c)(3) professional association for electronic engineering and electrical engineering (and associated disciplines) with its corporate office in New York City and its operati ...

Milestone award, 2009, for Philips only with the citation: "On 8 March 1979, N.V. Philips' Gloeilampenfabrieken demonstrated for the international press a Compact Disc Audio Player. The demonstration showed that it is possible by using digital optical recording and playback to reproduce audio signals with superb stereo quality. This research at Philips established the technical standard for digital optical recording systems."

Standard

The ''Red Book'' specifies the physical parameters and properties of the CD, the optical parameters, deviations and error rate, modulation system (

, EFM) and error correction facility ( cross-interleaved Reed–Solomon coding, CIRC), and the eight subcode channels. These parameters are common to all compact discs and used by all logical formats: audio CD, CD-ROM, etc. The standard also specifies the form of digital audio encoding (2-channel signed 16-

bit The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represented a ...

LPCM Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM stream, the a ...

sampled at

44,100 Hz In digital audio, 44,100 Hz (alternately represented as 44.1 kHz) is a common sampling frequency. Analog audio is often recorded by sampling it 44,100 times per second, and then these samples are used to reconstruct the audio signal w ...

). The first edition of the ''Red Book'' was released in 1980 by

and

; it was adopted by the Digital Audio Disc Committee and ratified by the

International Electrotechnical Commission The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and ...

(IEC) Technical Committee 100 as an international standard in 1987 with the reference IEC 60908. The second edition of IEC 60908 was published in 1999 and it replaces the first edition, amendment 1 (1992) and the corrigendum to amendment 1. The IEC 60908 however does not contain all the information for extensions that is available in the Red Book, such as the details for CD-Text,

CD+G CD+G (also known as CD-G, CD+Graphics and TV-Graphics) is an extension of the compact disc standard that can present low-resolution graphics alongside the audio data on the disc when played on a compatible device. CD+G discs are often used for ...

and CD+EG. The standard is not freely available and must be licensed. It is available from Philips and the IEC. , Philips outsources licensing of the standard to Adminius, which charges for the ''Red Book'', plus each for the ''Subcode Channels R-W'' and ''CD Text Mode'' annexes.

Audio format

The audio contained in a CD-DA consists of two-channel signed 16-

sampled at

and written as a

little-endian In computing, endianness, also known as byte sex, is the order or sequence of bytes of a word of digital data in computer memory. Endianness is primarily expressed as big-endian (BE) or little-endian (LE). A big-endian system stores the most ...

interleaved stream with left channel coming first. The

sampling rate In signal processing, sampling is the reduction of a continuous-time signal to a discrete-time signal. A common example is the conversion of a sound wave to a sequence of "samples". A sample is a value of the signal at a point in time and/or sp ...

is adapted from that attained when recording digital audio on

videotape Videotape is magnetic tape used for storing video and usually sound in addition. Information stored can be in the form of either an analog or digital signal. Videotape is used in both video tape recorders (VTRs) and, more commonly, videocasse ...

with a

, an earlier way of storing digital audio. An audio CD can represent frequencies up to 22.05 kHz, the

Nyquist frequency In signal processing, the Nyquist frequency (or folding frequency), named after Harry Nyquist, is a characteristic of a sampler, which converts a continuous function or signal into a discrete sequence. In units of cycles per second ( Hz), i ...

of the 44.1 kHz sample rate. There was a long debate over the use of 16-bit (Sony) or 14-bit (Philips) quantization, 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 (DAC), but Sony insisted on 16-bit. In the end Sony won, so 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 In signal processing, oversampling is the process of sampling a signal at a sampling frequency significantly higher than the Nyquist rate. Theoretically, a bandwidth-limited signal can be perfectly reconstructed if sampled at the Nyquist rate ...

. Some CDs are mastered with

pre-emphasis Typically, prior to some process, such as transmission over cable, or recording to phonograph record or tape, the input frequency range most susceptible to noise is boosted. This is referred to as "pre-emphasis"before the process the signal will u ...

, an artificial boost of high audio frequencies. The pre-emphasis improves the apparent signal-to-noise ratio by making better use of the channel's dynamic range. On playback, the player applies a de-emphasis filter to restore the frequency response curve to an overall flat one. Pre-emphasis time constants are 50µs and 15µs (9.49 dB boost at 20 kHz), and a binary flag in the disc subcode instructs the player to apply de-emphasis filtering if appropriate. Playback of such discs in a computer or

ripping Ripping is extracting all or parts of digital content from a container. Originally, it meant to rip music out of Commodore 64 games. Later, the term was used to extract WAV or MP3 format files from digital audio CDs, but got applied as well to ...

to WAV files typically does not take into account the pre-emphasis, so such files play back with a distorted frequency response.

Storage capacity and playing time

The creators of the CD originally aimed at a playing time of 60 minutes with a disc diameter of 100 mm (Sony) or 115 mm (Philips). Sony vice-president

suggested extending the capacity to 74 minutes to accommodate the recording of

Wilhelm Furtwängler Gustav Heinrich Ernst Martin Wilhelm Furtwängler ( , , ; 25 January 188630 November 1954) was a German conductor and composer. He is widely regarded as one of the greatest symphonic and operatic conductors of the 20th century. He was a major ...

conducting

Ludwig van Beethoven Ludwig van Beethoven (baptised 17 December 177026 March 1827) was a German composer and pianist. Beethoven remains one of the most admired composers in the history of Western music; his works rank amongst the most performed of the classic ...

's Ninth Symphony at the 1951

Bayreuth Festival The Bayreuth Festival (german: link=no, Bayreuther Festspiele) is a music festival held annually in Bayreuth, Germany, at which performances of operas by the 19th-century German composer Richard Wagner are presented. Wagner himself conceived ...

. The additional 14-minute playing time subsequently required changing to a 120 mm disc.

, 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 onto one of the earliest CDs. According to a ''

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 t ...

'' interview, the story is slightly more involved. In 1979, Philips owned

PolyGram PolyGram N.V. was a multinational entertainment company and major music record label formerly based in the Netherlands. It was founded in 1962 as the Grammophon-Philips Group by Dutch corporation Philips and German corporation Siemens, to be ...

, one of the world's largest distributors of music. PolyGram had set up a large experimental CD plant in

, Germany, which could produce huge numbers of CDs having 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. 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. The 74-minute playing time of a CD, which is longer than the 22 minutes per side typical of long-playing (LP)

vinyl album A phonograph record (also known as a gramophone record, especially in British English), or simply a record, is an analog sound storage medium in the form of a flat disc with an inscribed, modulated spiral groove. The groove usually starts near ...

s, 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 instead offer less audio than the LP. One such example was with

DJ Jazzy Jeff & The Fresh Prince DJ Jazzy Jeff & the Fresh Prince were an American hip hop duo from West Philadelphia, Pennsylvania, consisting of rapper Will Smith (the Fresh Prince) and disc jockey Jeff Townes ( DJ Jazzy Jeff). Active full time from 1986 to 1994 and occas ...

's double-album '' He's the DJ, I'm the Rapper'', in which initial CD releases of the album had multiple tracks edited down for length to fit on a single disc; recent CD reissues package the album across two discs as a result. The emergence of 80-minute CDs allowed for some double albums that were previously edited for length or packaged as double-CDs to be re-released on a single disc, such as ''

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'' by

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in the case of the former and ''

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'' by

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in the case of the latter. Playing times beyond 74 minutes are achieved by decreasing track pitch (the distance separating the track as it spirals the disc). However, most players can still accommodate the more closely spaced data if it is still within ''Red Book'' 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. In current practice, maximum CD playing time has crept higher by reducing minimum engineering tolerances.

Technical specifications

Data encoding

Each audio sample is a signed 16-bit

two's complement Two's complement is a mathematical operation to reversibly convert a positive binary number into a negative binary number with equivalent (but negative) value, using the binary digit with the greatest place value (the leftmost bit in big- endian ...

integer An integer is the number zero (), a positive natural number (, , , etc.) or a negative integer with a minus sign ( −1, −2, −3, etc.). The negative numbers are the additive inverses of the corresponding positive numbers. In the language ...

, with sample values ranging from −32768 to +32767. The source audio data is divided into frames, containing twelve samples each (six left and six right samples, alternating), for a total of 192 bits (24 bytes) of audio data per frame. This stream of audio frames, as a whole, is then subjected to CIRC encoding, which segments and rearranges the data and expands it with

error correction code In computing, telecommunication, information theory, and coding theory, an error correction code, sometimes error correcting code, (ECC) is used for controlling errors in data over unreliable or noisy communication channels. The central idea i ...

s in a way that allows occasional read errors to be detected and corrected. CIRC encoding interleaves the audio frames throughout the disc over several consecutive frames so that the information will be more resistant to burst errors. Therefore, a physical frame on the disc will actually contain information from multiple logical audio frames. This process adds 64 bits of

data to each frame. After this, 8 bits of subcode or subchannel data are added to each of these encoded frames, which is used for control and addressing when playing the CD. CIRC encoding plus the subcode byte generate 33-bytes long frames, called "channel-data" frames. These frames are then modulated through

(EFM), where each 8-bit word is replaced with a corresponding 14-bit word designed to reduce the number of transitions between 0 and 1. This reduces the density of physical pits on the disc and provides an additional degree of error tolerance. Three "merging" bits are added before each 14-bit word for disambiguation and synchronization. In total there are 33 × (14 + 3) = 561 bits. A 27-bit word (a 24-bit pattern plus 3 merging bits) is added to the beginning of each frame to assist with synchronization, so the reading device can locate frames easily. With this, a frame ends up containing 588 bits of "channel data" (which are decoded to only 192 bits of music). The frames of channel data are finally written to disc physically in the form of pits and lands, with each pit or land representing a series of zeroes, and with the transition points—the edge of each pit—representing a 1. A Red Book-compatible

has pit-and-land-shaped spots on a layer of organic dye instead of actual pits and lands; a laser creates the spots by altering the reflective properties of the dye. Due to the weaker error correction sector structure used on audio CDs and

video CD Video CD (abbreviated as VCD, and also known as Compact Disc Digital Video) is a home video format and the first format for distributing films on standard optical discs. The format was widely adopted in Southeast Asia, Central Asia and the ...

s ('' Mode 2 Form 2'') than on data discs (''Mode 1'' or ''Mode 2 Form 1''), C2 errors are not correctable and signify data loss. Even with uncorrectable errors, a compact disc player interpolates the

data loss Data loss is an error condition in information systems in which information is destroyed by failures (like failed spindle motors or head crashes on hard drives) or neglect (like mishandling, careless handling or storage under unsuitable conditions) ...

with the aim of making the damage unhearable.

Data structure

The audio data stream in an audio CD is continuous, but has three parts. The main portion, which is further divided into playable audio tracks, is the ''program area''. This section is preceded by a ''lead-in'' track and followed by a ''lead-out'' track. The lead-in and lead-out tracks encode only silent audio, but all three sections contain subcode data streams. The lead-in's subcode contains repeated copies of the disc's Table of Contents (TOC), which provides an index of the start positions of the tracks in the program area and lead-out. The track positions are referenced by absolute

timecode A timecode (alternatively, time code) is a sequence of numeric codes generated at regular intervals by a timing synchronization system. Timecode is used in video production, show control and other applications which require temporal coordinatio ...

, relative to the start of the program area, in MSF format: minutes, seconds, and fractional seconds called ''frames''. Each timecode frame is one seventy-fifth of a second, and corresponds to a block of 98 channel-data frames—ultimately, a block of 588 pairs of left and right audio samples. Timecode contained in the subchannel data allows the reading device to locate the region of the disc that corresponds to the timecode in the TOC. The TOC on discs is analogous to the

partition table Disk partitioning or disk slicing is the creation of one or more regions on secondary storage, so that each region can be managed separately. These regions are called partitions. It is typically the first step of preparing a newly installed disk, ...

hard drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magne ...

s. Nonstandard or corrupted TOC records are abused as a form of CD/DVD copy protection, in e.g. the key2Audio scheme.

Tracks

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 still support this feature have become rarer over time. The vast majority of songs are recorded under index 1, with the pre-gap being index 0. Sometimes

hidden track In the field of recorded music, a hidden track (sometimes called a ghost track, secret track or unlisted track) is a song or a piece of audio that has been placed on a CD, audio cassette, LP record, or other recorded medium, in such a way as to ...

s are placed at the end of the last track of the disc, often using index 2 or 3, or using the pre-gap as index 0 (this latter usage will result in the track playing as the time counter counts down to time 0:00 at the start of the track, index 1.) 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 An information society is a society where the usage, creation, distribution, manipulation and integration of information is a significant activity. Its main drivers are information and communication technologies, which have resulted in rapid info ...

's ''

Hack Hack may refer to: Arts, entertainment, and media Games * ''Hack'' (Unix video game), a 1984 roguelike video game * ''.hack'' (video game series), a series of video games by the multimedia franchise ''.hack'' Music * ''Hack'' (album), a 199 ...

'' was one of very few CD releases to do this, following a release with an equally obscure

feature.) The track and index structure of the CD were carried forward to the DVD format as title and chapter, respectively. Tracks, in turn, are divided into timecode frames (or sectors), which are further subdivided into channel-data frames.

Frames and timecode frames

The smallest entity in a CD is a channel-data ''frame'', which consists of 33 bytes and contains six complete 16-bit stereo samples: 24 bytes for the audio (two bytes × two channels × six samples = 24 bytes), eight CIRC error-correction bytes, and one subcode byte. As described in the "Data encoding" section, after the EFM modulation the number of bits in a frame totals 588. On a ''Red Book'' audio CD, data is addressed using the ''MSF scheme'', with

s expressed in minutes, seconds and another type of ''frames'' (mm:ss:ff), where one frame corresponds to 1/75 of a second of audio: 588 pairs of left and right samples. This timecode frame is distinct from the 33-byte channel-data frame described above, and is used for time display and positioning the reading laser. When editing and extracting CD audio, this timecode frame is the smallest addressable time interval for an audio CD; thus, track boundaries only occur on these frame boundaries. Each of these structures contains 98 channel-data frames, totaling 98 × 24 = 2,352 bytes of music. The CD is played at a speed of 75 frames (or sectors) per second, thus 44,100 samples or 176,400 bytes per second. In the 1990s, CD-ROM and related Digital Audio Extraction (DAE) technology introduced the term ''

sector Sector may refer to: Places * Sector, West Virginia, U.S. Geometry * Circular sector, the portion of a disc enclosed by two radii and a circular arc * Hyperbolic sector, a region enclosed by two radii and a hyperbolic arc * Spherical sector, a p ...

'' to refer to each timecode frame, with each sector being identified by a sequential

number starting at zero, and with tracks aligned on sector boundaries. An audio CD sector corresponds to 2,352 bytes of decoded data. The ''Red Book'' does not refer to sectors, nor does it distinguish the corresponding sections of the disc's data stream except as "frames" in the MSF addressing scheme. The following table shows the relation between tracks, timecode frames (sectors) and channel-data frames:

Bit rate

The audio

bit rate In telecommunications and computing, bit rate (bitrate or as a variable ''R'') is the number of bits that are conveyed or processed per unit of time. The bit rate is expressed in the unit bit per second (symbol: bit/s), often in conjunction w ...

for a ''Red Book'' audio CD is 1,411,200 bits per second (1,411 kbit/s) or 176,400

bytes per second In telecommunications and computing, bit rate (bitrate or as a variable ''R'') is the number of bits that are conveyed or processed per unit of time. The bit rate is expressed in the unit bit per second (symbol: bit/s), often in conjunction w ...

; 2 channels × 44,100 samples per second per channel × 16 bits per sample. Audio data coming in from a CD is contained in sectors, each sector being 2,352 bytes, and with 75 sectors containing 1 second of audio. For comparison, the bit rate of a "1×" CD-ROM is defined as 2,048 bytes per sector × 75 sectors per second = 153,600 bytes per second. The remaining 304 bytes in a sector are used for additional data error correction.

Data access from computers

Unlike on a DVD or CD-ROM, there are no " files" on a ''Red Book'' audio CD; there is only one continuous stream of

audio data, and a parallel, smaller set of 8 subcode data streams. Computer

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ef ...

s, however, may provide access to an audio CD as if it contains files. For example,

Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for ...

represents the CD's Table of Contents as a set of Compact Disc Audio track (CDA) files, each file containing indexing information, not audio data. By contrast however,

Finder Finder may refer to: * Finder (surname) * Finder (software), part of the Apple Macintosh operating system * ''Finder'' (comics), a comic book series by Carla Speed McNeil * ''Finder'' (novel), a 1994 novel by Emma Bull * Finder Wyvernspur, a fi ...

macOS macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac (computer), Mac computers. Within the market of ...

presents the CD's content as an actual set of files, with the

AIFF Audio Interchange File Format (AIFF) is an audio file format standard used for storing sound data for personal computers and other electronic audio devices. The format was developed by Apple Inc. in 1988 based on Electronic Arts' Interchange Fil ...

-extension, which can be copied directly, randomly and individually by track as if it were actual files. In reality, macOS performs its own as-needed-rips in the background completely transparent to the user. The copied tracks are fully playable and editable on the user's computer. In a process called

, digital audio extraction software can be used to read CD-DA audio data and store it in files. Common

audio file format An audio file format is a file format for storing digital audio data on a computer system. The bit layout of the audio data (excluding metadata) is called the audio coding format and can be uncompressed, or compressed to reduce the file size, o ...

s for this purpose include WAV and AIFF, which simply preface the LPCM data with a short header;

FLAC FLAC (; Free Lossless Audio Codec) is an audio coding format for lossless compression of digital audio, developed by the Xiph.Org Foundation, and is also the name of the free software project producing the FLAC tools, the reference software p ...

ALAC ALAC may refer to: * Alcohol Advisory Council of New Zealand, autonomous Crown entity for promoting alcohol moderation * Aluminium acetate (AlAc), a number of different salts of aluminum with acetic acid * Apple Lossless Audio Codec, an audio cod ...

, and Windows Media Audio Lossless, which compress the LPCM data in ways that conserve space yet allow it to be restored without any changes; and various

lossy In information technology, lossy compression or irreversible compression is the class of data compression methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data size ...

, perceptual coding formats like

AAC AAC may refer to: Aviation * Advanced Aircraft, a company from Carlsbad, California * Alaskan Air Command, a radar network * American Aeronautical Corporation, a company from Port Washington, New York * American Aviation, a company from Cleveland, ...

, and

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, which modify and compress the audio data in ways that irreversibly change the audio, but that exploit features of human hearing to make the changes difficult to discern.

Format variations

Recording publishers have created CDs that violate the ''Red Book'' standard. Some do so for the purpose of copy prevention, using systems like

Copy Control Copy Control was the generic name of a copy prevention system, used from 2001 until 2006 on several digital audio disc releases by EMI Group and Sony BMG Music Entertainment in several regions (Europe, Canada, United States, and Australia). I ...

. Some do so for extra features such as

DualDisc The DualDisc is a type of double-sided optical disc product developed by a group of record companies including MJJ Productions Inc., EMI Music, Universal Music Group, Sony BMG Music Entertainment, Warner Music Group, and 5.1 Entertainment Group a ...

, which includes both a CD layer and a DVD layer whereby the CD layer is much thinner, 0.9 mm, than required by the ''Red Book'', which stipulates a nominal 1.2 mm, but at least 1.1 mm. Philips and many other companies have stated that including the Compact Disc Digital Audio logo on such non-conforming discs may constitute trademark infringement.

Super Audio CD Super Audio CD (SACD) is an optical disc format for audio storage introduced in 1999. It was developed jointly by Sony and Philips Electronics and intended to be the successor to the Compact Disc (CD) format. The SACD format allows multiple ...

was a standard published in 1999 that aimed to provide better audio quality in CDs.

DVD Audio DVD-Audio (commonly abbreviated as DVD-A) is a digital format for delivering high-fidelity audio content on a DVD. DVD-Audio uses most of the storage on the disc for high-quality audio and is not intended to be a video delivery format. The st ...

emerged at around the same time. The format was designed to feature audio of higher fidelity. It applies a higher sampling rate and uses 650 nm lasers. Neither format was widely accepted.

Copyright issues

There have been moves by the

recording industry A record, recording or records may refer to: An item or collection of data Computing * Record (computer science), a data structure ** Record, or row (database), a set of fields in a database related to one entity ** Boot sector or boot record, r ...

to make audio CDs (Compact Disc Digital Audio) unplayable on computer CD-ROM drives, to prevent the copying of music. This is done by intentionally introducing errors onto the disc that the embedded circuits on most stand-alone audio players can automatically compensate for, but which may confuse CD-ROM drives. Consumer rights advocates as of October 2001 pushed to require warning labels on compact discs that do not conform to the official Compact Disc Digital Audio standard (often called the Red Book) to inform consumers which discs do not permit full

fair use Fair use is a doctrine in United States law that permits limited use of copyrighted material without having to first acquire permission from the copyright holder. Fair use is one of the limitations to copyright intended to balance the intere ...

of their content. In 2005,

Sony BMG Music Entertainment Sony BMG Music Entertainment was an American record company owned as a 50–50 joint venture between Sony Corporation of America and Bertelsmann. The venture's successor, the revived Sony Music, is wholly owned by Sony, following their buyou ...

was criticized when a copy protection mechanism known as Extended Copy Protection (XCP) used on some of their audio CDs automatically and surreptitiously installed copy-prevention software on computers (see Sony BMG copy protection rootkit scandal). Such discs are not legally allowed to be called CDs or Compact Discs because they break the Red Book standard governing CDs, and Amazon.com for example describes them as "copy protected discs" rather than "compact discs" or "CDs".

References

External links

Philips' Audio Standards licensing info

IEC 60908:1999 Audio recording – Compact disc digital audio system

MultimediaWiki article about PCM and ''Red Book'' CD Audio
{{Authority control Audiovisual introductions in 1980 Audio storage IEC 60908 Japanese inventions Dutch inventions Joint ventures Rainbow Books