Compact Disc Digital Audio
The Compact Disc Digital Audio ( CD -DA short, audio compact disc or audio CD) is an optical mass storage, which was developed in 1979 by Philips and Sony for digital storage of music. It replaced within a few years the record as the most important for Sale particular medium of recorded speech and music recordings from. In 1992, also known as CD-R came in trade, to provide consumers with a CD recorder or a personal computer itself can play music, which was often used for copying purchased CDs.
- 6.1 Serial Copy Management System
- 6.2 Non- compliance with the standard method 6.2.1 legal
- 6.2.2 Technical Details
- 6.2.3 Problems and consequences
A few years after the launch of the CD in 1982, the digital medium was more popular than the vinyl record; in the U.S. alone approximately 30,000 CD players and 800,000 audio CDs were sold in 1983. 1988 100 Millionen Audio CDs per year were produced for the first time.
In the early 1990s then disappeared LPs mostly from the former " record stores ". Millions of buyers replaced their partially decades built up record collections by audio CDs and allowed the music industry to record sales after years of recession. The boom in the German music industry was in 1997, when the industry generated about 2.6 billion euros.
In Germany Audio CDs - at least for tax purposes - not considered as a valuable cultural assets; for audio CDs applies a VAT rate of 19 percent, while this is for books and notes at 7 per cent.
However, since around the turn of the millennium the record companies complain again declining sales. The drop in sales are up to ten percent; German record companies lost even one-fifth of its sales in 2003; in 2002, sales had already fallen by more than eleven percent to less than two billion euros.
Causes of the current problems of the music industry should be according to her especially black copies that are distributed through file sharing networks, as well as copies of audio CDs. In " Vinyl - age" music could be copied only with tape recording devices such as cassette tapes, which coincided with each additional copy with more or less loss of quality. With today's digital media however, loss-free and identical copies are possible.
According to the music industry, the number of pre-recorded music CD blanks on climb (2002: 267 million ) of the selling music CDs ( 2002: 166 million ) by far; how these numbers should have been determined, the representatives of the music industry does not reveal, however. Critics accuse the music industry, the corporations would have the signs of the times - for example, the development of a consistent sales as internet download - overslept and would now be in damage control ( consumer- hostile copy protection measures, criminal proceedings against Internet music file sharing, campaigning with the slogan " pirates are practicing criminal " ).
Another reason is the reluctance of some consumers to buy music of poor quality and low value creation. Furthermore, not all downloaded tracks found their 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 (see Rainbow Books ) are described in the so-called colored books and allowed to carry the Compact Disc logo. The format specifications of the audio CD, properly known as CD-DA, was standardized in 1980 under the name Red Book by the ANSI (IEC -908 ); this standard made it possible that originally each CD and each CD -ROM drive could play any audio CD - as long as the record companies stopped the norm.
An audio CD contains in this original form only audio data and no multimedia or textual additional information. However, extensions to the CD -DA such as Mixed Mode CD, Enhanced CD / CD -Plus, CD - Text, CD G or CD MIDI may contain additional information.
The audio data is stored uncompressed. The Red Book format only supports a simple method for detecting or correcting reading errors, the so-called Cross -interleaved Reed -Solomon code (CIRC ), and allowed up to 250 errors per second. Good CD players can still (almost ) overlap somewhat higher error numbers inaudible.
CD itself is a 1.2 mm thick disc with a diameter of 12 cm or 8 cm ( CD single ), which consists of a polycarbonate substrate on which a thin aluminum layer is applied.
The audio data at a sampling rate of 44.1 kHz, 16 -bit values and with two channels ( left, then right) recorded; the data rate of an audio CD, however, is higher than 1411200 bits / s, as for each case 24 bytes of the audio payload data, an additional byte is recorded with so called Subkanaldaten.
The bandwidth of an audio CD is 5 Hz to 20 kHz, the dynamic range at 96 dB. In this case, the reconstructed analog audio signal with appropriate implementation of the digital -to-analog converter is in principle completely decoupled from the quality of the data carrier, as long as the user data is error-free.
The data is combined into data records, which are called the small frame. Each small frame contains 33 bytes. Of these 24 bytes of audio data (exactly six stereo samples ), 8 bytes of error correction data, and a so-called subcode byte. The bits of the sub-code bytes will be referred to as P -W. The respective bits of the successive sub-code bytes each form a so-called Subchannel. The individual subchannels are also denoted by P to W.
Every 98 Small - frames to form a block ( also called sector or frame ) summarized. Thus, each block contains 2352 bytes audio data. This corresponds to 1 /75 seconds or 588 samples (samples). The 98 subcode bytes makes the eight sub - channels P to W to 98 bits each. The audio CD by the Red Book standard uses only the subchannel P and Q. P subchannel contains a simple music - pause flag. This can be used by CD players to skip breaks. This feature is not supported by some devices.
Q subchannel, however, contains a wealth of information. The 98 Q -channel bits of a block have the following structure:
- 2 Bit synchronization
- 4-bit ADR - Specifies that contains data of the Q -channel in this sector: 0 = Q- channel data
- 1 = position information ( see below)
- 2 = Media Catalog Number ( UPC or EAN for example )
- 3 = ISRC
- 4 to 15 = Reserved
- Bit 0: 1 = Audio data with pre-emphasis; 0 = no
- Bit 1: 1 = Digital copy permitted; 0 = Digital copy prohibited
- Bit 2: 1 = data track; 0 = audio track
- Bit 3: 1 = four-channel audio ( quadraphonic ); 0 = two-channel audio (stereo)
If the Q -channel contains position information, these are encoded 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 may contain various data, such as can be seen in Figures 4 ADR bits can not contain its position information of each sector. If a sector contains no location information or verification with the CRC checksum of the Q subchannels can detect a read error, most CD players indicate an interpolated value. According to Red Book standard, however, have nine out of ten sectors contain position information, so stand while playing a CD very quickly new location information.
Subchannel R to W are unused for pure audio CDs and are ignored by most audio CD players. Extended formats, such as CD Text or CD G code where their additional data.
On an audio CD up to 99 tracks can be stored. A trace corresponds usually a piece of music. Each track can also be divided by up to 99 index points further ( for example, the movements of a symphony or opera arias within a ), but today's playback devices support this function frequently not more, since it was used only on a few CDs.
A standard track must be at least four seconds ( 300 sectors), index points must also have at least four seconds apart. Is the track pre-gap, which in standards-compliant audio CD has a length of at least two seconds must have and must have the audio quiescent level between tracks. However, many audio CDs contain tracks that merge into each other seamlessly, without an audible gap between them.
The addressing of sectors is in sympathy with the purpose of use as a sound carrier: The sectors are in the format minute: second: frame addressed. This addressing is called MSF format. These data are coded in BCD stored on the CD to simplify the display. The value for seconds is on 0-59, the frame number on 0-74. There are thus block addresses from 00:00:00 to 99:59.74 possible, which is adequate for the originally -designed game time of 74 minutes. It is determined that the first track to start at sector 00:00:00. Certain areas of the CD are, however, before the first track and therefore require negative sector numbers. These are stored with an offset of 100 minutes, so they fall into the unused address ranges from 80:00.00 until 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, such as the Table Of Content ( TOC) to display their content when the drive allows.
The sectors of an audio CD have no header. It is therefore not possible to specifically to control and read individual sectors. In order to identify which sector is being read, the drive needs to read one, sometimes even several sectors and analyze the data of the Q - channel. This explains the rather long access time during random driving about another track.
Low- level format
The data bits are not pressed directly into the pits and lands on the CD. The data on an 8-to -14- encoding in so-called channel bits are instead converted. Is the channel bits of a data byte are also still long by 3 bits breaks ( engl. gap) separated so per data byte of the space needed that of 17 channel bits.
The 33 bytes of a mini frames correspond to 33 × 8 = 264 bits. 33 × 17 561 channel bits, however, are stored on the CD =. These then are still 24 channel bits for synchronization and three so-called merge bits, ie 588 channel bits per frame mini. A second playing time on an audio CD are 7350 mini frames.
For details about how the data is stored on the CD, see the article compact disc
The key for the playing time of the CD diameter was established 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, the engineers made the CD 5 mm larger.
The length of recording on an audio CD is set after lengthy discussions between Sony and Philips to 74 minutes. First, the developer of Philips had proposed a disc with a record time of one hour. Here intervened Sony's Norio Ohga personally Vice President: In a meeting with the development team of Philips CD - he argued that the most important works of Mozart and Beethoven typically lasted about 60 minutes. Then the developers of Philips saw a that classical music could be marketed reasonable if the pieces fit on a disc. According Ohga Herbert von Karajan but I - never even intervened in the length of discussion - contrary to popular legends.
The " odd" sample rate of 44.1 kHz was reached by the following circumstance: The digital audio data needed a storage medium that had to be reliable and available. That was prevalent at that time in the studio - - For this purpose, a video recorder system from U -Matic Sony was used because it was able to save correspondingly high-frequency digital signals permanently on magnetic tape. There were special converter (PCM-1610 and PCM -1630 ), the audio data is digitized with 16-bit and a " video " signal generated, which could be recorded by the U -Matic VCR. Pro video image line were 96-bit to be coded. At 294 useful lines and 50 frames per second ( the fields of the PAL video signal ) were able to 294 × 96 × 50 = 1,411,200 bits are stored per second. At 2 × 16 bits per sample, there was such a sampling rate of 44,100 samples per second.
Especially on older CDs indicates whether the individual receiving steps ( recording, mixing, pre-master ) have been created analog or digital. These abbreviations AAD, ADD, DAD, and DDD can be used.
Extra-long audio CDs
As the specifications contains certain tolerances of the physical format ( about the track pitch ), it is possible ( narrower writing the tracks) to accommodate these tolerances by Ausreizen more data on a CD, as was originally intended.
While exhibited at the start of mass production of CD blanks that have the same basic structure as an audio CD, this a playing time of 74 minutes, they are manufactured today usually so that they have about 80 minutes of playing time.
Also pressed audio CDs after the Red Book standard nowadays have increasingly seasons over 74 minutes; especially in the field of classical music. As the specifications allow (ie 360 000 data sectors plus lead-in and lead-out ) a maximum playing time until 79:59.74 sector, these audio CDs do not hurt the Red Book and may thus carry the CD logo. From almost all CD players such discs are played back smoothly.
A further increase of track density allows an even longer time (90 or 99 minutes, according to 405 000 or 445 500 sectors). Here, the Red Book specifications are violated, however, since the allowed tolerances are exceeded in the track density and thus provide increased demands on the accuracy of the tracking. In addition, sector addresses are used in these media, which have been reserved by the CD Red Book standard for the negative sector addresses of contents (TOC). Since many CD drives only regard the sectors over 90:00.00 as a negative sector addresses are so-called 90 - minute blanks (ie those sectors until 89:59.74 included) on these drives still playable. The so-called 99 -minute blank, however, require a certain amount of "intelligence" of the drive electronics to detect whether a negative or a sector address is meant the end of the CD. In practice, a heuristic is used mostly that works as follows: A selective reading of addresses between 90 and 99 provides the data on the CD early (negative addresses ), a continuous reading of CD with increasing addresses is recognized, however, and it the sectors read during the transition from 89 minutes to 90 at the end of the CD. Because of the problems, the 90 - and 99 cause - minute blanks, rather discouraged by this, because you can not be sure whether they can be read later on another drive again.
Serial Copy Management System
Similar to the DAT standard audio CD for the Red Book standard contains a copy protection method, where only the Table of Contents Table of Contents ( TOC), a bit indicating the copy protection. In addition, there is a similar bit in each Q -sub -channel block, which can show three states (see SCMS ):
- Copy bits are set at a frequency of 9.375 Hz alternating on 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 thus itself can not be copied
- Copy- bits are always set (" 1-1 " ) - it may arbitrarily many copies are made. The copy protection bits remain unchanged.
Theoretically should be correctly output on the digital output at a hi-fi CD player these flags. However, in most computer components these flags are ignored.
A with a frequency of 9.375 Hz (50 % duty cycle ) alternating copy bit was originally intended to signal that the current copy was made by a person who does not have the necessary rights of copyright. Among others, but Sony has begun to bring commercial CDs on the market, which are provided with the alternate copy bit.
Non- compliance with the standard method
Since about 2001, Audio CDs are sold in Germany that use beyond this method. Since these CDs no longer correspond to the Red Book standard, they may not carry a CD-DA logo. Based on the standard deviation they can no longer play in all CD players. These CDs are often referred to by critics as "Un - CDs ".
However, such CDs must be clearly marked d Copyright Act by the manufacturer since 1 November 2003 in accordance with § 95. The IFPI (International Federation of the Phonographic Industry ) has introduced a logo for copy-protected audio CDs. The Heise magazine publisher operating a database that could be searched for copy-protected and potentially unplayable music CDs. After most of the CDs were shipped but again without copy protection mechanisms, it was decided in mid-2009, to take the side back of the net.
The circumvention of "effective copy protection " is after the amendment of the copyright law (New Copyright Act ( Copyright Act ), in force since 13 September 2003) is no longer permitted ( § 95 a of the Copyright Act ). Here, however, the question arises whether the copy protection method used for audio CDs ever meet the demand for an effective copy, as many CD drives can automatically correct these errors. A judicial decision on the copy of the audio CD is still pending. In everyday life, the right to bypass the copy is indeed considered to be purely private purposes as illegal, but is still not a criminal offense ( de minimis rule ).
Not as a bypass counts, not to take effect the copy protection only. For example, can the copy protection MediaMax CD3 SunnComm under the operating system Microsoft Windows can cancel by pressing the Shift key, as it will have CD autorun is turned off. Under Mac OS X, and Linux and other free systems of this copyright protection does not work anyway.
Numerous methods are used, intended to prevent copying an audio CD, with different protection and efficiency. All these methods have in common that they've interfere with or prevent the reading and playing of the data, but not the subsequent copying. The manufacturers of these methods, however, assume that the modifications (generally easier) control logic of an audio CD player is not so very disturbing, like that of a more complex CD-ROM drive in a computer. As for digital copying usually a CD -ROM drive is used to read the data, copy the data would thus be impossible. In addition, the method can not distinguish between a (usually legal) home or backup one hand, and an illegal copy of the other.
- Illegal TOC (Table of Contents - Table of Contents ): (usually in an additional session), the track positions on illegal (illegal ) deflected positions, such as on a block in the lead-in to this process. Pure CDDA players usually read only the first session containing the audio data according to the Red Book standard. Thus, this protection applies only to multi-session capable drives Another type of illegal TOC manifests itself with a changing every time you insert the CD track list. TOC is repeatedly on the CD, especially in order to avoid reading errors. Here a variety of different ( and wrong ) TOC are stored.
- Deliberate Read error: By manipulating the CIRC be distorted in places the piece of music with an approximately linear increase in the level of some sample data. The checksum is calculated, however, about the correct block. Thus, the respective samples are marked as defective during the reading of the block. Computer drives, which have no special audio mode, return the erroneous data, while hi- drives are specially prepared for such errors and (often linearly ) interpolate the erroneous data. As the level increases linearly at the point to this error on hi-fi players not be audible. However, it should be noted that in many blocks, the error correction is already maxed out. Each small scratches on the surface can provoke real read error. You buy it were an audio CD that is already defective from the outset.
- Incorrect Q- subcode: This copy is rarely used, since pure CDDA player so that may have problems. It is based on that CD player to play the CD similar to a LP in a single pass by follow this track. Only at the track selecting or skipping individual places a particular block is searched effectively. For audio CDs, the respective position in each Q- subcode to a block noted. If there enters a slightly different position ( messed rolls ), can not be exactly wanted, but not too disruptive pure CDDA player (only those with Shock Protection ). Computer drives, however, are usually addressed in blocks and must very often re- locate the position on the CD. This is no longer possible, since the positions are jumbled and therefore a couple of blocks is read before or later. This manifests itself in short repetitions or missing pieces (usually 0.05 seconds ).
Problems and consequences
However, since in a growing number of consumer electronics so-called combo drives are installed, which can read a variety of CD and DVD formats (eg MP3 CDs, Mixed Mode CDs), this means that non-standard Audio CDs from these devices can not be played correctly. The proliferation of these devices, thereby increasing playability issues of non-standard CDs has led to increasingly reach since 2008, Audio CDs, without such measures in the trade.
Contents and Formats
The known record of the marketing division into major and minor LPs singles has also been adopted in the audio CD. The following content-based formats emerged:
- CD ( Albums, Compilations ): recordings with 12 cm diameter and about 45 to 80 minutes of music / sound material
- Single: recordings with 8 cm diameter and about one to four pieces. Time is of the order of 12-15 minutes ( music)
- Maxi / Maxi - Single: Media 12 cm in diameter, but only about one to five pieces
In addition, the promo CD was, for advertising purposes a phonogram with twelve or eight centimeters in diameter, which is usually distributed free of charge. Sometimes it contains the whole album to be advertised, but sometimes only a very few pieces, or only parts of the whole piece. Target groups for promotional CDs are acting as multipliers people or institutions, such as radio stations and DJs.
The first audio CDs
The first audio CD set the record label PolyGram on August 17, 1982 in Langenhagen near Hannover before; it was inter alia to
- Waltz by Frédéric Chopin for piano, played by Claudio Arrau and
- The album The Visitors of the music group ABBA.
As in Europe at that time, however, were no CD players on the market, these CDs were only published in November 1982 in Japan. When first released audio CD of the story is true Billy Joel's album 52nd Street that brought Sony Music Entertainment together with the player CDP -101 on October 1, 1982 in Japan on the market.
Economics of audio CD
Towards the purchase of audio CDs and for downloading via peer-to -peer networks on the Internet is often cited, audio CDs are too expensive a consumer, because the listening habits of consumers have changed: Have you previously yet aware music heard - for example, allowed to run the turntable and heard from the chair of a symphony - you hear today, in the era of very small players such as MP3 players or Discmen, at every opportunity music, such as on the way to work, while jogging or during the working itself. So the consumers are not as strong as it used to be willing to pay for something that is consumed by the way, such high prices. That one among friends exchange music and that for this reason would decrease the purchases of music CDs per person, is a logical consequence of it.
Even against the composition of a CD sale price criticism is loud. According to the IFPI, the International Federation of the Phonographic Industry, make the licenses for the music " usually more than one third of the selling price to the retail trade of " necessary and is also a risk assessment, that is, cross-subsidization of successful CDs in favor of other productions, " because only 10-20 percent of all new publications play their own expense ." It is also clarified that the pure material and production costs of a CD would practically be zero.
Price composition of a CD music album in Germany:
The labels ( music companies ) also pay a separate amount to the artist. It is assumed that the artist receives 15 percent of the CD retail price.
Given the falling popularity of the audio CD and the problem of black copier is thinking about alternatives. It is argued that it would be possible to download a single song at a cost of 50 cents that the music company takes up about 40 percent of the price, while the artist, 20 percent also deserves more - because the manufacturing and distribution costs can be saved because the goods would be delivered over the Internet; GEMA compensation would be eliminated, because taxes were planned on the purchase of recordable media or already enacted. At 20 songs to 50 cents, the customer would pay in most cases less than when buying a real audio CD. Finally, think of a consistent proponent download music trade that the legitimate purchase of music would be boosted by the reduction of the consumer price.
The consumer partially felt strong increase in the average final price of recorded music can so far not be confirmed statistically. Thus, the price of sound recordings including music videos increased according to a study by the Federal Statistical Office when comparing the years 1993 and 2003 in nominal terms by 5.6 %, but declined in real terms (taking Inclusive of inflation) increased by 10.6 %.
In the 2007 Christmas season in the U.S., the largest music market in the world, declined, sales of CD albums by 21 percent the previous year. In the year 2007 511 Millionen CD albums were sold in the U.S., which is 17 percent less than in 2006. Revenues declined by 20 percent to 7.45 billion U.S. dollars. The CD single was recovering from the low of 1.7 million to 2.6 million pieces (sales: $ 12.2 million ).