Compact disc digital audio
Compact disc digital audio
|Optical storage medium
|12 cm / 8 cm (diameter)
|Philips , Sony
|Record , compact cassette
|Super audio CD , DVD audio
The compact disc digital audio ( CD-DA for short , also audio compact disc or audio CD ) is an optical mass storage device that was developed by Philips and Sony for the digital storage of music since 1979 . Within a few years it superseded the record as the most important sales medium for recorded voice and music recordings. The CD-DA has been standardized in the “ Red Book ” since 1983 .
Until the 1990s, “Compact Disc” or “CD” was synonymous with audio CD.
In 1992, so-called blank CDs came on the market, onto which consumers can play music themselves using a CD recorder or a personal computer , which was often used to copy purchased CDs. A few years later, such burning devices had become the normal standard in PCs, with prices falling from initially over 1000 DM into the lower double-digit range over time.
As a prehistory of the actual CD development, there were various approaches to optical digital data recording, including music and video data, in the 1970s, some of which led to patents (in the USA James T. Russell and David Paul Gregg ). At Philips , Klaas Compaan proposed the use of optical recording for video in 1969.
In the 1970s, technicians from many electronics companies were doing research in the field of digital audio recording. The first prototypes were based on magnetic storage media such as the classic audio cassette . The first device on the market was in 1977 an extension of the Betamax - VCR company Sony to a analog to digital - or digital to analog converter ( PCM modulator and demodulator). Instead of a video signal, the video recorder records the PCM signal, which - through appropriate coding in lines or images (frames) - looks like a video signal from the point of view of a video recorder. (The PCM coding process was later also adopted by the successor DVD-Audio .) The bulky device and the background noise during the recording could not convince the consumers. Sony developed special procedures to eliminate the background noise. In order to test these procedures, recordings were secretly made during a rehearsal of a concert by Herbert von Karajan in September 1978. Karajan was later invited by Sony to judge the recordings.
At the same time, Lou Ottens' team was working at Philips on the optical recording of image signals, which was to revolutionize video technology. I.a. the optical disc was presented at the radio exhibition in Berlin , which had roughly the format of an LP and was played by a correspondingly large player. The idea of using this technology for digital sounds soon developed. Both companies suddenly faced a problem. They had planned the new optical data carrier ( laser disc ), similar to the record, with a diameter of 30 cm. When recording moving images, they were able to fit around 30 minutes of video material on it. With audio data, however, the capacity was sufficient for 13 hours and 20 minutes. Sony knew that the music industry's business model would collapse if such amounts of music were to be marketed to consumers. After the compact cassette (audio cassette) had been developed by the Philips company alone in 1963, the two companies tried to bring about a common standard. The diameter of the CD, which is decisive for the playing time, was justified by the Philips leadership as follows: The compact cassette was a great success, the CD should not be much larger. The compact cassette had a diagonal of 11.5 cm, at the end the CD was 0.5 cm larger. Sony originally preferred a smaller diameter (10 cm). All sorts of modern legends have grown up about the definition of these parameters; one of the most popular is the following:
After some differences, Sony suggested that the new CD should at least capture Ludwig van Beethoven's Ninth Symphony in full. According to legend, this proposal was linked to Sony's then Vice-President Norio Ōga , who was a trained opera singer and had always wished to be able to hear Beethoven's Ninth without having to change the sound carrier. Ōga's favorite version, conducted by Herbert von Karajan, lasts 66 minutes, the technicians stuck to the longest version available at the time by Wilhelm Furtwängler . The recording from 1951 has a playing time of exactly 74 minutes. 74 minutes meant that the optical disk was twelve centimeters in diameter. The developers at Philips would have reacted with skepticism, since such a large pane would not fit in the suit pockets. Sony developers then measured suits from all over the world, with the result that there was room for twelve centimeters everywhere. According to this legend, Beethoven and Furtwängler would have set a new standard.
According to another version, it was Ōga's wife who insisted. A similar version of the story is officially distributed by Philips; However, according to one of the Philips developers involved at the time, Kees A. Schouhamer Immink, Beethoven's influence on CD playing time is a legend that was invented by the company's public relations departments, albeit partly with a real background (Philips obtained information at daughter Polygram, and the longest record time was that of Beethoven's ninth with Furtwängler). In reality, the developers at Sony and Philips met in 1979 and agreed on a diameter of 115 mm (whereby the most diverse arguments and parameters played a role, including the code used), but the company management of Philips and Sony decided on 120 mm in May 1980 and thus passed over the developers. According to Immink, the reason for the change to 12 cm was that Philips would have had a competitive advantage with 11.5 cm, as their production systems were already set up for things that did not suit Sony. Both the diameter and the cycle time were defined before the line code was established. As part of the development, experiments were recently carried out with a coding that is a variant of a code patented by Ampex . The fact that Philips managed at the last minute to implement the 30% more efficient Eight-to-Fourteen Modulation (EFM) instead and include it in the standard, together with the 5 mm larger diameter, made it possible to increase the track width and bit cell length enlarge so that the production of the CDs can work with more generous tolerances.
An interesting side note is that with the introduction of the CD, the maximum playing time for data storage in through the term of the mastering process using U-matic was fixed cassettes to 72 minutes. It was not until 1988, when alternatives to data storage became available, that Beethoven's Ninth could be placed in the Furtwängler version on a CD.
The "crooked" sampling rate of 44.1 kHz was due to the following circumstance: The U-matic from Sony, which was widespread in the studio at the time, stored correspondingly high-frequency digital signals permanently on magnetic tape. There were special converters (PCM-1610 and PCM-1630) that digitized audio data with 16 bits and generated a "video" signal that could be recorded by the U-Matic video recorder. 96 bits could be encoded per video image line. With 294 usable lines and 50 frames per second (the fields of the PAL video signal), 96 × 294 × 50 = 1,411,200 bits per second could be saved. With 2 × 16 bits per sample, this resulted in a sampling rate of 44,100 values per second.
In 1980, Philips and Sony established the Red Book standard for audio recordings . The diameter of the inner hole of the CD (15 mm) was determined by the Dutch Philips developers rather by chance. The smallest coin in the world at the time, the Dutch ten-cent piece (the so-called Dubbeltje ), which a developer had with him when determining the diameter, served as a benchmark . The CD was presented to the public for the first time at the 1981 radio exhibition in Berlin. The following year, on August 17, 1982, in Langenhagen near Hanover , in the production facilities of what was then Polygram , the world's first industrial production of the last ABBA album The Visitors began , even before October 1, 1982 with the Sony CDP. 101 the first mass-produced CD player could be offered on the market. In 1983 a compact disc cost between DM 30 and 45 , and around 700 titles were available. In the same year around 70,000 CD players were sold in the Federal Republic of Germany , the purchase price of which in 1984 was between 650 and 1,800 DM. In 1988, 100 million audio CDs were produced worldwide. From this year there were systems with which CDs could be burned.
Sales figures 1984–1991 and 2001–2019 in the Federal Republic of Germany:
(without CD single)
Note: The year of the largest sales is highlighted in gray.
Just a few years after the CD was launched in 1982, the digital medium became more popular than the vinyl record; In 1983, around 30,000 CD players and 800,000 audio CDs were sold in the United States alone. In 1988, 100 million audio CDs were produced annually for the first time.
In the early 1990s, LPs then largely disappeared from the former "record stores". Millions of buyers replaced their record collections, some of them built up over decades, with audio CDs, thus enabling the music industry to achieve record sales after years of recession . The boom year of the German music industry was 1997, when the industry generated around 2.6 billion euros.
However, since around the turn of the millennium, record companies have been complaining about declining sales. The slump in sales is up to 10 percent; German record companies even lost a fifth of their sales in 2003; in 2002 sales had already fallen by more than 11 percent to less than two billion euros.
According to the music industry, it is mainly black copies that cause problems that are distributed via file sharing networks , as well as copies of audio CDs. Tracks could only be copied from vinyl records using tape recorders such as a tape recorder. B. on music cassettes , which was accompanied by a loss of quality with each subsequent copy. With digital media, on the other hand, loss-free or identical copies are possible.
According to the music industry, the number of blank CDs recorded with music (2002: 267 million) far exceeds that of music CDs sold (2002: 166 million); The representatives of the music industry do not reveal how these figures are supposed to have been determined. Critics accuse the music industry that the corporations have overslept the signs of the times - for example the development of a systematic distribution as Internet downloads - and are now limiting themselves to damage (anti-consumer copy protection measures, criminal proceedings against Internet music exchanges, campaigns with the slogan “are pirates Criminals ”).
Another reason is the reluctance of some consumers to buy music of poor quality and low creative value. In addition, not every downloaded title will find its way onto a blank CD, but will be deleted after the first listen.
Technology and standardization
The audio CD is one of the official CD formats that are described in the so-called colorful books (see Rainbow Books ) and that are allowed to carry the compact disc logo. The format specifications of the audio CD, correctly called CD-DA , were standardized in 1980 under the name Red Book by ANSI IEC-908; this standard made it possible that originally every CD player and every CD-ROM drive could play every audio CD - as long as the manufacturer of the CD adhered to the standard.
In its original form, an audio CD only contains audio data and no additional multimedia or textual information. Extensions to CD-DA such as Mixed Mode CD, Enhanced CD / CD-Plus, CD + MIDI, CD + G or CD-Text can contain additional information that can be read by the normal file system of the computer operating system . This can lead to playback problems as soon as non-standard copy protection is used.
The audio data is saved uncompressed. The Red Book format only supports a simple procedure for recognizing or correcting reading errors, the so-called Cross-Interleaved Reed-Solomon Code (CIRC), and allows up to 250 errors per second. Good CD players can (almost) inaudibly cover up slightly higher numbers of errors.
The audio data is recorded with a sampling rate of 44.1 kHz (44,100 times per second), as 16-bit values and with two channels (stereo, first left, then right). This corresponds to 1,411,200 bit / s or the usual specified 1,411 kbit / s. The data transfer rate of an audio CD is somewhat higher, however, as an additional byte with so-called subchannel data is recorded for every 24 bytes of audio user data .
The bandwidth of an audio CD is 5 Hz to 20 kHz, the dynamic range is 96 dB . With a corresponding implementation of the digital-to-analog converter , the reconstructed analog audio signal is in principle completely decoupled from the quality of the data carrier as long as the useful data is available without errors.
The data is summarized in data sets called small frames . Each small frame contains 33 bytes. Of these, 24 bytes are audio data ( i.e. exactly six stereo samples), 8 bytes contain error correction data and a so-called subcode byte. The bits of the subcode byte are designated P to W. The respective bits of the successive subcode bytes each form a so-called subchannel . The individual subchannels are also labeled P to W.
98 small frames are combined into a block (also called a sector or frame). Each block thus contains 2352 bytes of audio data. This corresponds to 1/75 of a second or 588 samples. The 98 subcode bytes result in the eight sub-channels P to W of 98 bits each. The audio CD according to the Red Book standard only uses subchannels P and Q. Subchannel P contains a simple music pause flag . This can be used by CD players to skip pauses. However, this feature is not supported by some devices.
Subchannel Q, on the other hand, contains a lot of information. The 98 Q-Channel bits of a block have the following structure:
- 2 bit synchronization
- 4 bit ADR - Indicates which data the Q-Channel contains in this sector:
- 4 bit control bits
If the Q-Channel contains position information, it is coded as follows:
- 8 bit track number
- 8 bit index point
- 24 bit sector address (relative to the beginning of the track)
- 8 bits reserved (0)
- 24 bit absolute sector address
- 16 bit CRC checksum
Since the Q-Channel can contain different data, as can be seen from the 4 ADR bits, not every sector can contain its position information. If a sector does not contain any position information or the verification with the CRC checksum of the Q subchannel reveals a read error, most CD players display an interpolated value. According to the Red Book Standard, however, nine out of ten sectors must contain position information so that new position information is available very quickly when a CD is played.
Up to 99 tracks can be stored on an audio CD. A track usually corresponds to a piece of music. Each track can also be further subdivided by up to 99 index points (for example for the movements of a symphony or arias within an opera ), but today's playback devices often no longer support this function because it was only used on a few CDs.
A standard-compliant track must be at least four seconds (300 sectors) long, index points must also be at least four seconds apart. The track pre-gap is located between the tracks , which for standard-compliant audio CDs must be at least two seconds long and must have the audio quiescent level. However, many audio CDs contain tracks that merge seamlessly without an audible pause between them.
The addressing of the sectors is based on the intended use as a sound carrier: The sectors are addressed in the format minute : second : frame . This addressing is called MSF format. To simplify the display, this data is BCD-coded and stored on the CD. The value for seconds is from 0–59, the frame number from 0–74. Block addresses from 00: 00.00 to 99: 59.74 are possible, which is sufficient for the originally designed playing time of 74 minutes. It is specified that the first track should start at sector 00: 00.00. However, certain areas of the CD are located before the first track and therefore require negative sector numbers. These are saved with an offset of 100 minutes so that they fall into the unneeded address ranges from 80: 00.00 to 99: 59.74. An MSF value of 97: 30.00 corresponds to a time position of −2.5 minutes on the CD. Many CD diagnostic programs are able to read these sectors and their content, such as B. to display the Table Of Content (TOC), if the drive allows this.
The sectors of an audio CD do not contain a header. It is therefore not possible to target and read out individual sectors. In order to recognize which sector is currently being read, the drive has to read one, sometimes even several sectors and evaluate the data of the Q-Channel. This explains the rather long access time when randomly controlling another track, for example.
The data bits are not pressed directly onto the CD in pits and lands. Instead, the data is converted into so-called channel bits via 8-to-14 coding . The channel bit of a data byte are also much longer by 3 bit intervals (engl. Gap ) is required so that separated per data byte space of 17 channel bits.
The 33 bytes of a small frame correspond to 33 × 8 = 264 data bits. However, 33 × 17 = 561 channel bits are stored on the CD. In addition to these, there are 24 channel bits for synchronization and three so-called merge bits , i.e. 588 channel bits per small frame. One second of playing time on an audio CD corresponds to 7350 small frames.
For more information on how the data is stored on the CD, see the Compact Disc article .
Oversized audio CDs
Since the specifications contain certain tolerances of the physical format (such as the track spacing), it is possible, by exhausting these tolerances (closer writing of the tracks), to accommodate more data on a CD than was originally intended.
While blank CDs - which have the same basic structure as an audio CD - had a playing time of 74 minutes at the beginning of mass production, today they are usually manufactured in such a way that they have a playing time of around 80 minutes.
Pressed audio CDs according to the Red Book standard also increasingly have playing times over 74 minutes; especially in the field of classical music. Since the specifications allow a maximum playing time up to sector 79: 59.74 (i.e. 360,000 data sectors plus lead-in and lead-out), these audio CDs do not violate the Red Book and may therefore bear the CD logo. Almost all CD players can play such CDs without any problems.
A further increase in the track density allows an even longer playing time (90 or 99 minutes, corresponding to 405,000 or 445,500 sectors). However, this violates the specifications of the Red Book, since the permitted tolerances for the track density are exceeded and thus place increased demands on the accuracy of the track guidance. In addition, sector addresses are used on these media which have been reserved by the Red Book standard for the negative sector addresses of the table of contents (TOC) of the CD. Since many CD drives only treat the sectors above 90: 00.00 as negative sector addresses, so-called 90-minute blanks (which contain sectors up to 89: 59.74) can still be played on these drives. The so-called 99-minute blanks , on the other hand, require a certain “intelligence” from the drive electronics in order to recognize whether a negative sector address or one at the end of the CD is meant. In practice, a heuristic is usually used that works as follows: A targeted reading of addresses between 90 and 99 supplies the data at the beginning of the CD (negative addresses), whereas continuous reading of the CD with increasing addresses is recognized and it is at the transition from minute 89 to 90, the sectors are read out at the end of the CD. Due to the problems caused by 90- and 99-minute blanks, these are not advisable since you cannot be sure whether they can be read later on another drive.
Serial Copy Management System
Similar to the DAT standard, the audio CD contains a copy protection method according to the Red Book standard , with only one bit in the table of contents (TOC) indicating copy protection. In addition, there is a similar bit in every Q-Sub-Channel block, which can indicate three states (see SCMS ):
- Copy bits with a frequency of 9.375 Hz alternately set over the sub-channel blocks ("1-0") - means that no digital copy may be made
- Copy bits always unset ("0-0") - means that a digital copy may be made in which the copy protection bits are set alternately and therefore cannot be copied
- Copy bits always set ("1-1") - any number of copies can be made. The copy protection bits remain unchanged.
A copy bit alternating with a frequency of 9.375 Hz (50% clock ratio) was originally intended to signal that the current copy was made by a person who does not have the necessary copyright rights. Among other things, Sony has started to sell commercial CDs that are provided with the alternating copy bit.
Since around 2001 audio CDs have also been sold that use additional processes. Since these CDs no longer comply with the Red Book standard, they are not allowed to bear the CD-DA logo. Due to the deviation from the norm, they can no longer be played in all CD players .
In Germany, however, such CDs have had to be clearly marked by the manufacturer since November 1st, 2003 according to § 95 d UrhG. The IFPI ( International Federation of the Phonographic Industry ) has introduced a corresponding logo for copy-protected audio CDs. The Heise magazine publisher operating a database that could be searched for in the copy-protected and potentially unplayable music CDs. When most of the CDs were delivered again without copy protection mechanisms, it was decided in mid-2009 to take the site off the Internet again.
The circumvention of an “ effective copy protection ” is no longer permissible after the amendment to copyright law ( New Copyright Act ( UrhG ), in force since September 13, 2003) (Section 95 a UrhG). However, the question arises as to whether the copy protection methods used for audio CDs even meet the requirement for effective copy protection, since many CD drives can automatically correct these errors. A court decision on the copy protection of audio CDs is still pending.
In Germany, circumventing copy protection for purely private purposes is regarded as illegal in everyday legal life, but is still not a criminal offense (trivial clause). It does not count as a workaround to simply not let the copy protection take effect. For example, the copy can MediaMax CD3 of SunnComm under the operating system Windows simply by pressing the Shift disable because hereby the CD autostart is turned off. Under macOS as well as Linux and other free systems, this copy protection does not work anyway due to the different type of access to the optical drive.
In Switzerland, it is legal to remove copy protection for private use.
Numerous methods are used to prevent an audio CD from being copied, with varying degrees of protection and efficiency. All these methods have in common that they interfere with or prevent the reading out and playback of the data, but not the subsequent copying. However, the manufacturers of these methods assume that the modifications do not interfere with the (generally simpler) control logic of an audio CD player as much as that of a more complex CD drive in a computer. Since a CD-ROM drive is usually used to read the data for digital copying, copying the data would be made impossible. In addition, the procedures cannot differentiate between a (usually legal) private or security copy on the one hand and an illegal copy on the other.
- Illegal TOC (Table of Contents): With this procedure, the track positions are redirected (usually in an additional session ) to impermissible (illegal) positions, such as a block in the lead-in. CDDA-only players normally only read the first session, which according to the Red Book standard contains the audio data. This protection therefore only applies to multi-session-capable drives.
Another type of illegal TOC manifests itself with a track list that changes each time the CD is inserted. The TOC is written on the CD several times in a row, mainly to prevent reading errors. A large number of different (and incorrect) TOCs are stored here.
- Intentional reading errors: By manipulating the CIRC , some sample data are falsified at points in the piece of music with an almost linear increase in level. However, the checksum is calculated over the correct block. This means that the respective samples are marked as defective when the block is read out. Computer drives that do not have a special audio mode return the faulty data, while HiFi drives are specially prepared for such errors and interpolate the faulty data (often linearly). Since the level increases linearly at this point, this error should not be audible on hi-fi players. However, it should be noted that the error correction has already been exhausted in many blocks. Every small scratch on the surface can provoke real reading errors. You buy an audio CD, so to speak, that is already defective from the start.
- Incorrect Q subcodes : This copy protection is rarely used because pure CDDA players can also have problems with it. It is based on the fact that CD players play the CD in one go, similar to an LP, in that they follow the track. A specific block is only effectively searched for when selecting a track or when skipping individual positions. In the case of audio CDs, the respective position is noted in each Q subcode for a block. If you enter a slightly different position there (mixed up), you can no longer search exactly, but this does not bother pure CDDA players (only those with shock protection). Computer drives, on the other hand, are usually addressed in blocks and very often have to search again for the position on the CD. This is then no longer possible because the positions are mixed up and therefore read a few blocks before or later. This manifests itself in short repetitions or missing bits (usually around 0.05 seconds long).
Problems and Consequences
However, since so-called combination drives are being built into more and more entertainment electronics devices, which can read a variety of CD and DVD formats (e.g. MP3 CDs, mixed mode CDs ), audio CDs that do not conform to standards are also being used can no longer be played correctly by these devices. The increasing spread of these devices and the increasing problems with playing CDs that do not conform to standards has led to the fact that since 2008 audio CDs have been increasingly coming onto the market again without such measures.
Contents and formats
The marketing division into large LPs and smaller singles known from vinyl records was also adopted for the audio CD. The following content-dependent formats were created:
- CD ( albums , compilations ): sound carrier with a diameter of 12 cm and about 45 to 80 minutes of music / sound material
- Single : Sound carrier with a diameter of 8 cm and about one to four pieces. Playing time in the order of 12 to 15 minutes (music)
- Maxi / Maxi single: Sound carrier with a diameter of 12 cm, but only about one to five pieces
In addition, the promo CD was created , a sound carrier with a diameter of twelve or eight centimeters for advertising purposes, which is usually distributed free of charge. Sometimes it contains the entire album that is to be advertised, but sometimes only a very few pieces or only excerpts from the whole pieces. The target groups for promo CDs are people or institutions who act as multipliers, for example radio stations or DJs .
The first audio CDs
- An Alpine Symphony by Richard Strauss , played by the Berliner Philharmoniker under the direction of Herbert von Karajan ,
- Waltz by Frédéric Chopin for piano , played by Claudio Arrau as well
- the album The Visitors by the music group ABBA .
Since there were no CD players on the market in Europe at that time, these CDs were not released in Japan until November 1982 . The first published audio CD in history is Billy Joel's album 52nd Street , which Sony Music Entertainment released on October 1, 1982 in Japan together with the CDP-101 player.
Economy of the audio CD
According to the World Association of the Sound Carrier Industry ( IFPI ), the licenses for the music "usually make up more than a third of the retail price " and there is cross-subsidization of successful CDs in favor of other CDs, "because only 10-20 percent of all new releases are costly a".
|Record companies ("Labels")
|Sales tax (Germany)
According to a study by the Federal Statistical Office, the price for sound carriers and music videos increased nominally by 5.6% between 1993 and 2003, and thus decreased in real terms (taking inflation into account) by 10.6%.
In the 2007 Christmas business in the USA, the world's largest music market, sales of CD albums fell by 21 percent compared to the previous year. In 2007, 511 million CD albums were sold in the USA, 17 percent less than in 2006. Sales fell by 20 percent to 7.45 billion US dollars. The CD single recovered from the low 1.7 million to 2.6 million pieces (sales: 12.2 million dollars).
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