
#REDIRECT Compact disc
A compact disc (or CD) is an optical disc used to store digital data, originally developed for storing digital audio. A standard compact disc, often known as an ''audio CD'' to differentiate it from later variants, stores audio data in a format compliant with the Red Book (audio CD standard) standard. An audio CD consists of several stereo tracks stored using 16-bit Pulse-code modulation coding at a sampling rate of 44.1 kHz. Standard compact discs have a diameter of 120mm, though 80mm versions exist in circular and "business-card" forms. The 120mm discs can hold 74 minutes of audio, and versions holding 80 or even 90 minutes have been introduced. The 80mm discs are used as "CD-singles" or novelty "business-card CDs". They hold about 20 minutes of audio. Compact disc technology was later adapted for use as a data storage device, known as a CD-ROM. == History == In the early 1970s, using video Laserdisc technology, Philips' researchers started experiments with 'audio-only' optical discs, initially with wideband frequency modulation FM and later digitized Pulse-code modulation audio signals. At the end of the 70s, Philips, Sony, and other companies presented prototypes of digital audio discs. In 1979 Philips and Sony decided to join forces, setting up a joint taskforce of engineers whose mission it was to design the new digital audio disc. Prominent members of the taskforce were Kees A. Schouhamer Immink and Toshi Doi. After a year of experiment and discussion the taskforce produced the 'Red Book (audio CD standard)', the Compact Disc standard. Philips contributed the general manufacturing process, based on the (unsuccessful) video Laserdisc technology. Philips also contributed the Eight-to-Fourteen Modulation, EFM, which offers both a large playing time and a high resilience against disc handling damage such as scratches and fingerprints; while Sony contributed the error-correction method, CIRC. The [http://www.exp-math.uni-essen.de/~immink/pdf/cdstory.pdf Compact Disc Story,] told by a former member of the taskforce, gives background information on the many technical decisions made, including the choice of the sampling frequency, playing time, and disc diameter. According to Philips, the Compact Disc was thus "invented collectively by a large group of people working as a team."[http://www.research.philips.com/newscenter/dossier/optrec/index.html] The Compact Disc reached the market in 1983, and this event is often seen as the 'Big Bang' of the digital audio revolution. The new audio disc was enthusiastically received and its handling quality received particular praise. From its origins as a music format, Compact Disc has grown to encompass other applications. Two years later, in 1985, the CD-ROM (read-only memory) was introduced. With this it was now possible to disseminate massive amounts of computer data instead of digital sound. A user-recordable CD for data storage, CD-R, was introduced in the early 1990s, and it became the de facto standard for exchange and archiving of computer data and music. The CD and its later extensions have been extremely successful: in 2004 the annual worldwide sales of CD-Audio, CD-ROM, and CD-R reached about 30 billion discs. == Physical details == Compact discs are made from a 1.2 millimetre thick disc of polycarbonate plastic coated with a much thinner layer of Super Purity Aluminium Aluminium (originally gold, which is sometimes still used for its data longevity) layer which is protected by a film of lacquer. The lacquer can be printed with a label. Common printing methods for compact discs are silkscreening and offset printing. CDs are available in two sizes. By far the most common is 120 mm in diameter, with a 74 minute audio capacity and a 650 MB data (See #Storage capacity). They are also available as 80 mm discs, a format which is mainly used for audio CD singles in some regions (like Japan), much like the old single (music). Each such "miniCD" or "Maxi CD" can hold 21 minutes of music, or 180 MB of data. There is 15 mm hole in the centre of the disc, usually used by a some form of clamp or clip device within the player to hold it in place and allow it to be rotated by a motor. The information on a standard CD is encoded as a spiral track of ''pits'' moulded into the top of the polycarbonate layer (The areas between pits are known as ''lands''). Each pit is approximately 125 nanometre deep by 500 nm wide, and varies from 850 nm to 3.5 micrometre long. The spacing between the tracks is 1.6 μm. To grasp the scale of the pits and land of a CD, if the disc is enlarged to the size of a stadium, a pit would be approximately the size of a grain of sand. The spiral begins at the center of the disc and proceeds outwards to the edge, which allows the different size formats available. A CD is read by focusing a 780 nm wavelength semiconductor laser through the bottom of the polycarbonate layer. The difference in height between pits and lands is one quarter of the wavelength of the laser light, leading to a half-wavelength phase difference between the light reflected from a pit and from its surrounding land. The destructive interference this reduces the intensity of the reflected light compared to when the laser is focused on just a land. By measuring this intensity with a photodiode, one is able to read the data from the disc. The pits and lands themselves do not represent the zeroes and ones of binary data. Instead a change from pit to land or land to pit indicates a one, while no change indicates a zero. This in turn is decoded by reversing the Eight-to-Fourteen Modulation used in mastering the disc, finally revealing the raw data stored on the disc. == Audio format == The format of the audio disc, known as the 'Red Book (audio CD standard)' standard, was laid out by SONY and Philips in 1981. Philips is responsible for the licensing program of the intellectual property pertinent to the Compact Disc including the 'CDDA' logo that appears on the disc. In broad terms the format is a two-channel (four-channel sound is an allowed option within the Red Book format) stereo 16-bit Pulse-code modulation encoding at a 44.1 kHz sampling rate. Reed-Solomon error correction allows the CD to be scratched to a certain degree and still be played back. The sampling rate of 44.1 kHz is inherited from a method of converting digital audio into an analog video signal for storage on video tape, which was the most affordable way to store it at the time the CD specification was being developed. A device that turns an analog audio signal into PCM audio, which in turn is changed into an analog video signal is called a PCM adaptor. This technology could store 6 samples (3 samples per each stereo channel) in a single horizontal line. A standard NTSC video signal has 245 usable lines per field, and 59.94 fields a second, which works out at 44,056 samples/second. Similarly PAL has 294 lines and 50 fields, which gives 44,100 samples/second. This system could either store 14-bit samples with some error correction, or 16-bit samples with almost no error correction. There was a long debate over whether to use 14 or 16 bit samples and/or 44.056 k or 44.1 k samples/s when the Sony/Philips taskforce designed the compact disc; 16 bits and 44.1 k samples/s prevailed. The Sony PCM-1610 and PCM-1630 are well-known examples of PCM-adaptors used in conjunction with the Sony U-Matic VCR. === Storage capacity === The main parameters of the CD (taken from the September 1983 issue of the Red Book (audio CD standard)) are as follows: *Scanning velocity: 1.2-1.4 m/s (constant linear velocity). *Track pitch: 1.6 μm. *Disc diameter 120 mm. *Disc thickness: 1.2 mm. *Inner radius program area: 25 mm. *Outer radius program area: 58 mm. We find that the program area equals 86.05 square cm, so that the length of the recordable spiral is 86.05/1.6 = 5.38 km. Given a scanning speed of 1.2 m/s, we note that the playing time is 74 minutes, or around 650 MB of data on a CD-ROM. In case the disc diameter would have been 115 mm, the maximum playing time would have been 68 minutes, i.e., 6 minutes less. A disc with data appearing slightly more densely is allowable. Using a linear velocity of 1.2 m/s and a track pitch of 1.5 micrometre leads to a playing time of 80 minutes, or a capacity of 700 MB. This is the limit for most conventional audio CDs today. Another technique to increase the capacity of a disc is store data in the lead out groove that is normally used to indicate the end of a disk, and an extra minute or two of recording is often possible. However, these discs can cause problems in playback when the end of the disc is reached. === Subcode === Besides digital audio, a CD contains digital data called 'subcode', which is multiplexed with the digital audio. The data in a CD is arranged in frames. A frame comprises 33 bytes, of which 24 are audio bytes (six full stereo samples), eight error correction, CIRC-generated, bytes plus one subcode byte. The eight bits of a subcode byte are available for control and display. The eight bits are used as eight different subcoding channels, and given letters designating their usage: P, Q, ..., W. Thus each channel has a bit rate of 7.35 (=44.1/6) kbit/s. In each sector there are 2352 bytes (24 * 98) of audio content data and 96 bytes of subchannel data. The 96 bytes of subchannel information in each sector contain four packets of 24 bytes apiece : 1 byte for command, 1 byte for instruction, 2 bytes for parityQ, 16 bytes for data, and 4 bytes parityP. Each of the 96 subchannel data bytes can be thought of as being divided into 8 bits. Each of these bits corresponds to a separate stream of information. These streams are called "channels", and are labeled starting with the letter P, like so: {| cellpadding=3 |- |Channel |P |Q |R |S |T |U |V |W |- |Bit |7 |6 |5 |4 |3 |2 |1 |0 |} Channel P is a simple pause/music flag, which can be used for low-cost search systems. Quite a few players ignore it in favor of the Q Channel. Channel Q is used for control purposes of more sophisticated players. It contains positioning information, the Media Catalog Number, and International Standard Recording Code. The ISRC is used by the media industry, and contains information about the country of origin, the year of publication, owner of the rights, as well as a serial number, and some additional tags: ;Data: This track contains Data (rather than audio). Can be used for muting in audio CD Players. ;Copy Flag: Used by the Serial Copy Management System to indicate permission to digitally copy the track. ;Four Channel Compact Disc Digital Audio: The track uses four channel audio. This is very rarely used on Compact Discs. ;Pre-Emphasis: The audio track was recorded with pre-emphasis. Used very rarely on Compact Discs. Channels R..W are unused by red-book compliant CDs, and have been used for extensions to the standard. === CD-Text === CD-Text is an extension of the Red_Book_(audio_CD_standard) standard for audio CDs. It allows to store additional information (like album name, song name, artist,..) on a standards-compilant audio CD. The information is stored in the lead-in area of the CD (there's roughly 5 Kilobytes space there), or in the Subchannels R to W on the disc, which are not used on red-book compliant CDs. About 31 Megabytes of information can be stored there. The text is stored in a format usable by the Interactive Text Transmission System (ITTS). ITTS is also used by Digital Audio Broadcasting or the MiniDisc. Please note that other extensions like CD+G also use those subchannels to store graphics in. == The AAD, ADD, DDD code for audio CDs == Originally, audio-format CDs came with a three letter code on the back, where "A" stood for analog signal and "D" stood for digital. The first letter represented how the album had been recorded, the second how it had been mixed, and the third how it had been transferred. As a result, almost all early CDs are "AAD" (analog recording and mixing, digital transfer to CD). Often this code was accompanied by a short description such as "Full Digital Recording" for DDD and "Digitally Mixed Analog Recording" for ADD. Although experimental recordings exist from the 1960s, digital recording of classical and jazz music began to be made commercially in the early 1970s, pioneered by Japanese companies such as Denon; the first 16-bit PCM recording in the United States was made at the Santa Fe Opera in 1976 on a Soundstream recorder. In most such cases, there was no mixing stage involved; a stereo digital recording was made and used unaltered as the master tape for subsequent commercial release. These, and other subsequent unmixed digital recordings are still described as DDD, as the technology involved is purely digital. (Likewise, unmixed analog recordings are usually described as ADD, to denote a single generation of analog recording). The first digitally recorded and mixed (DDD) popular music album was ''Bop Till You Drop'' by Ry Cooder in 1978. Many other top recording artists, such as Stevie Wonder, were early adherents of digital recording. Others, such as former Beatles producer George Martin, felt that the multitrack digital recording technology of early 1980s had not reached the sophistication of analog systems; however, he used digital mixing to eliminate the distortion and noise that an analog master tape would introduce (thus ADD). An early example of an analog recording that was digitally mixed is ''Tusk (album)'' by Fleetwood Mac, from 1979. By the time the compact disc was introduced worldwide, digital recording and mixing was becoming commonplace among recording artists and producers known for their interest in fidelity. Two examples from 1982 are ''Signals (album)'' by Rush, and ''The Nightfly'' by Donald Fagen. A few examples of DAD recordings exist, mostly of tunes that were originally recorded digitally but later remixed by artists who preferred to work with analog technology. When it started making LPs and cassettes, the originally CD-only label Ryko extended this system to the other media, so that a digital recording on an LP would be DDA, and so forth. == CD-ROM == For its first few years of existence, the compact disc was purely an audio format. However, in 1985 Yellow Book (CD-ROM_standards) CD-ROM standard was established by Sony and Philips, which defined a non-volatile optical data computer storage medium using the same physical format as audio compact discs, readable by a computer with a CD-ROM drive. The smallest entity in the CD audio format is called a ''frame''. A frame can accommodate six complete 16-bit stereo samples, i.e. 2*2*6 = 24 bytes. Data in a CD-ROM are organized in both frames and sectors. A CD-ROM ''sector'' contains 98 frames, and holds 98*24 = 2352 bytes. The CD-ROM is in essence a data disc, which cannot rely on error concealment, and it requires therefore a higher reliability of the retrieved data. In order to achieve improved error correction and detection, a CD-ROM has a third layer of Reed-Solomon error correction. Note that the CIRC error correction system used in the CD audio format has two interleaved layers. A Mode-I CD-ROM, which has the full third layer error correction capability, contains a net 2048 bytes of the available 2352 per sector. In a Mode-2 CD-ROM, which is mostly used for video files, we have 2336 user-available bytes per sector. The net byte rate of a Mode-1 CD-ROM is 44.1*2048/(6*98) = 153.6 byte/s. The playing time is 74 minutes, or 4440 seconds, so that the net capacity of a Mode-I CD-ROM equals 682 Mbyte. == Recordability == Injection moulding is used to mass produce compact discs. A 'stamper' is made from the original media (audio tape, data disc, etc.) by writing to a glass disc (referred to as a glass master) coated with a photosensitive dye with a laser. This dye is then etched, leaving the data track. It is then plated to make a positive version of the CD. Polycarbonate is liquified and injected into the mold cavity where the stamper transfers the pattern of pits and lands to the polycarbonate disc. The disc is then metallized with aluminum and lacquer coated. Recordable compact discs are injection molded with a "blank" data spiral. A photosensitive dye is then applied, and then the discs are metallized and lacquer coated. The write laser of the CD recorder changes the characteristics of the dye to allow the read laser of a standard CD player to see the data as it would an injection molded compact disc. CD-R recordings are permanent. The resulting discs can be read by most CD-ROM drives and played in most audio CD players. CD-RW is a re-recordable medium that uses a metallic alloy instead of a dye. The write laser in this case is used to heat and alter the chemical properties of the alloy and hence change its reflectivity. A CD-RW does not have as great a difference in the reflectivity of lands and bumps as a pressed CD or a CD-R, but many CD audio players cannot read CD-RW discs, although the majority of standalone DVD players can. == Copy protection == The Red Book audio specification does not include any copy prevention mechanism. ''Ripping'' is the process by which the contents of an audio disc is copied out verbatim to a duplicate disc or re-encoded into some other format, such as MP3. An CIRC is included with Red Book audio to deal with small scratches or defects on the disc media. Where error correction fails on larger defects, audio CD players are expected to apply interpolation algorithms to conceal the loss of audio data. Starting in early 2002, attempts were made by record companies to market "copy-protected" compact discs. Some of these deliberately introduced error patterns into audio tracks severe enough to defeat the error-correcting code (and hence defeat most CD-ROM drives attempting to copy the tracks as data), but not so disruptive as to prevent interpolation from working (hence allowing the same tracks to be played in audio mode without overly affecting high fidelity). Another copy protection method places a data track (usually containing bonus software for computer users) at the end of the disc and gives it an invalid size in the disc's table of contents. This is intended to prevent the data track from ripped, but can be defeated by ignoring the table of contents and reading the disc sector by sector. Philips has stated that such discs are not permitted to bear the trademarked ''Compact Disc Digital Audio'' logo because they violate the Red Book specification. It also seems likely that Philips' new models of CD recorders will be designed to be able to record from these 'protected' discs. However, there has been great public outcry over copy-protected discs because many see it as a threat to fair use. Other systems developed are Macrovision CDS-200 and Mediamax CD-3. In any case, even if a disc cannot be directly ripped, it can still be played in audio mode, and the audio thence captured. Any loss of sound quality caused by this method is generally considered negligible. This is commonly referred to as the analog hole. == Non-standard CD behaviors == Some commercially-released audio discs have a "secret" hidden track. These may be an extension of the last audio track or a separate track hidden from the disc's table of contents. Either way, the hidden portion is heard when the disc is played to the end. One such track is "Her Majesty (song)", a bonus track included on The Beatles' ''Abbey Road (album)'' album disc. It starts after 20 seconds of total silence after the final listed track, "The End (The Beatles song)". Other discs hide the extra material at the beginning of the disc. On most discs, the location of the first track listed in the table of contents immediately follows the table of contents itself. In this case, the hidden track is an unlisted track sandwiched between the two. To hear the hidden track, the listener must usually "rewind" the player past the beginning of the first listed track. Not all players allow this. == Name == Notwithstanding the variability of general usage between disk or disc [http://www.bartleby.com/61/16/C0521600.html], the customary spelling is "compact disc", rather than "compact disk". This may be in large degree due to its status as a Philips trademark under that spelling. == References == * Kenneth C. Pohlmann (1992). ''The Compact Disc Handbook''. Middleton, Wisconsin: A-R Editions. ISBN 895793008. == See also == * CD-ROM * CD-R * CD-RW * Rainbow Books ** Red Book (audio CD standard) ** Yellow Book (CD-ROM standards) * CD-G * Enhanced CD * Video CD * SVCD * Jewel case * CD Wallet * CD Organizer * Digipak * miniCD * Optical disc ** DVD CD 120 mm discs Audio storage Video storage als:Compact Disc fa:لوح فشرده ga:Dlúthdhiosca simple:Compact disc
I hope to see the 1X unit of CD throughput defined here some day, also the 1X of DVD defined there. I'm guessing the [http://www.google.com/search?q=define:+1X "Google define: 1X"] claims of 1X CD = 150,000 byte/s and 1X DVD = 1,380,000 byte/s are slightly incorrect, because seemingly imprecise, because rounded decimally. (Pat LaVarre, 21st September 2004) ::CD audio has 176,400 bytes a second of data to be precise (44100 * 2 bytes (16 bits) * 2 channels (stereo)). The error correction overhead for a data CD is roughly 13% (derived by the number of bytes of data an 80 minute CD fits compared to the number of bytes of audio data if burned as an audio CD), so we get 153,333 bytes a second. User:Samboy 02:03, 10 Nov 2004 (UTC) ::CD (according to the article) can hold 650 MB or 74 minutes. So assuming that a cd drive can read 650 MB in 74 minutes at 1x, the 1x read speed of a 650MB data CD is 650MB / 74 min = 650MB / (74 x 60 sec.) = 146,396 B/s = 1.17 Mbit/s. If by MB the article was referring to 1024 KB (the article is unclear on this!), then multiplying by 1.024 x 1.024, the modified figures are 153,508 B/s = 1.23 Mbit/s. --User:Tokek 03:58, 29 Mar 2005 (UTC) :::650MB is the capacity for data mode, which has more redundancy than audio mode. VCDs and audio CDs are written without the added redundancy, and have a max size of about 735MB on a "650MB" CD. So on a data CD, you're actually reading in the redundancy data along with the user data, which creates the 13% of overhead in Samboy's derivation. (I believe MB in this case does refer to the powers of two variety. Are we ever going to start using "Mebibyte"?) - User:Mako098765 01:05, 30 Mar 2005 (UTC) ::::Right, audio is (176,400 B/s) * (74mins) = 783,216,000 B, data is 650 MiB = 681,574,400 B, data read speed is (176,400 B/s) * (681,574,400 B / 783,216,000 B) = 153,508 B/s = 1.228 Mbit/s. Different calculations (both took overhead into account btw), same results. --User:Tokek 07:16, 30 Mar 2005 (UTC) :::::I just wanted to point out that the CD drive reads in the same amount of raw data at 1x for audio as well as data. Perhaps the article could benefit from an overview of effective sector sizes in different data modes. - User:Mako098765 21:13, 30 Mar 2005 (UTC) ::::::Good work, but all this probably belongs on the CD-ROM page. --User:Dtcdthingy 00:40, 31 Mar 2005 (UTC) ---- ''A 120mm disc can store about 74 minutes of music or about 650 megabytes of data.'' :Is it true that 74 minutes length was decided to have enough room for Beethoven's 9th symphony? I couldn't find any definitive reference. ::Yes. The president of Sony at the time (some Japanenese guy whose name eludes me at the moment) was a huge Beethoven fan. He wanted the compact disc to be big enough to hold Beethoven's 9th symphony its entirety (so that he wouldn't have to change the disc), so he basically demanded that the engineers make it hold 74 minutes. User:Raul654 03:23, Jul 1, 2004 (UTC) :::There is a lot of urban legends about this entire thing, so I will point people to [http://www.snopes.com/music/media/cdlength.htm this page]. The general impression I get is that, yes, the length of Beethoven's 9th did increase the diameter by one centimeter so that a CD could fit all fo the 9th (which usually doesn't need 74 minutes, but needs more than 60 minutes, which is how much time we would have gotten if we didn't increase the diameter by a centimeter). User:Samboy 01:57, 10 Nov 2004 (UTC) ---- In my opinion, the discussion about disc vs. disk is a moot point because "compact disc" is a tradename not a generic name. What is with the disc vs. disk anyway? I have always used disk for a disk and disc when referring to something round. My spell checker seems to say that they can be both used for a tech disk though, odd. --User:Josquius 16:58, 20 May 2004 (UTC) You're right - despite what any dictionary says, the inventors of teh compact disc named it disc. It's a brand name. You don't accept "cleanex" as a correct spelling for "Kleenex", or "zerocks" for "Xerox". Disc it is disc it always has been, and disc it always shall be. Don't believe me, go look at the logo. It's on every CD jewel case. History, please! When was the CD created, 1983? CD-R, early 1990s? And the CD-RW? And how about a link to a more generic entry on data storage? Further, how did the engineers decide on the diameter? Was it to match the 5.25" floppy disks common in the early 1980s? Or was it to have enough room for an hour of music or for Beethoven's 9th Symphony? The CD was created in 1979. It was introduced to the U.S. in 1982. The first CD recorder was made by Yamaha and imported to the U.S. in 1988 (I was working for the company that imported it). CD-RW didn't come into being until about 1996. :The Philips trademark may spell it "disc", but that's not itself definitive as to general usage. The current article text is needlessly prescriptive; newspaper style guides are poor sources on such matters, since their purpose is internal consistency, not to determine the "only correct usage". If a section like this is even appropriate, better that it mention the trademark and the history, not seek to provide "usage notes" as the current text does. User:Alai 03:25, 20 Mar 2005 (UTC) :: It goes to show that some people consider the correct spelling to be very important. And from what I've seen, it's always been disc with a "c". I do agree that quoting the entire style guide entry is unnecessary; a small mention is sufficient. - User:Mako098765 08:26, 21 Mar 2005 (UTC) ---- The CD-ROM was pushed by Bill Gates? This needs a bit more info! - User:David Gerard 13:09, Jan 13, 2004 (UTC) : See Bill Gates User:Mikkalai 04:35, 27 Jan 2004 (UTC) ---- ''The advantage of MP3 is that it increases CD storage capacity by up to ten times without significant degradation in sound quality.'' That's likely to get an argument from some audiophiles! --User:Calieber 16:46, Feb 15, 2004 (UTC) ---- That intro is a tangled mess and not at all a good encapsulated summary of what a CD is and is for - the sort of thing that would make a useful concise article in itself. Anyone want to try a rewrite? - User:David Gerard 16:08, Mar 10, 2004 (UTC) ---- Hmm, the business-end of the CD is not depicted in a photo yet. User:Kim Bruning 14:09, 5 Apr 2004 (UTC) :I'm about to buy a digital camera ... mind you, I'll be on holiday with it for three weeks! Anyone? Anyone? - User:David Gerard 14:18, Apr 5, 2004 (UTC) ---- Interwiki rules: http://nl.wikipedia.org/wiki/Afbeelding:CompactDisc.jpg have a nice day :-) ---- ''For drives installed in computers, all current CD-ROM and DVD-ROM drives can read and write CD-R and CD-RW discs.'' This is nonsense. ''ALL'' is VERY false. Recordable drives are almost never called ROM drives. This implies that no more CD-ROM or DVD-ROM drives are made. Only CD-RW drives, DVD-ROM/CD-RW combo drives, Or DVD+/-R(W) (also DVD-ram) drives are made. Therefore I have removed this Statement from the main page. Feel free to correct it and place it back on the page. User:Tacvek 22:55, 15 Jun 2004 (UTC) I realize that CDs are constant linear velocity, but what are the general maximum and minimum speeds for reading at 1X (CD audio)? User:Ckape 22:46, 22 Sep 2004 (UTC) == sampling frequency == Explain why CDs have a sampling frequency of precisely 44.1KHz ::I have added the answer to the article: ::The reason why the unusual sampling rate of 44.1kHz was chosen was because, at the time the CD specification was being developed, the only way to make a reasonably affordable digital audio recorder was to convert digital audio in to a video signal, which was then recorded to a VCR. A NTSC video signal has 245 lines of resolution, updated 60 times a second; a PAL video signal has 294 lines of resolution, updated 50 lines a second. The technology could store 3 samples in a single horizontal line, either at 14 bits with some error correction, or at 16 bits with almost no error correction. There was a debate over whether to use 14 or 16 bit samples when they designed the compact disc; 16 bits prevailed. Hence, the decision to use the 16-bit, 44.1kHz sampling rate. The Sony PCM-1630, an early CD mastering machine, was just a modified U-Matic VCR User:Samboy 02:04, 10 Nov 2004 (UTC) :::Researching this a littlmore a raw NTSC signal has 525 lines of resolution, updated 30 times a second (the number is different above because of interlacing). Some of this signal is part of the vertical blank, but some of this signal is the invisible part used for storing closed captioning and what not. Everyone says that NTSC has 480 lines of visible resolution, but the people who made those old PCM encoders (mainly Sony) figured out some way to get another ten lines in there somehow. I can't find any details online, but I guess they used part of the signal made invisible for closed captioning purposes and what not. User:Samboy 13:39, 20 Dec 2004 (UTC) :::: The vertical sync signal between each field is quite complex, spread out over several lines. I presume 245 is the maximum number of lines that VCRs would reliably record; and that would leave enough room for a reasonably valid sync signal in between that would not confuse a VCR. :::: The 525 lines figure actually just means 1 line lasts 1/525th of 1/30th of a second, it doesn't account for blanking interval. I guess the 480 lines figure comes from digitizing NTSC video. :::: User:Dtcdthingy 19:53, 20 Dec 2004 (UTC) :::::I think the 480 line figure also comes from people being conservative about the number of scan lines in a NTSC signal that contain actual picture information. The people that say "480 lines" are usually making digital TVs and what not; they mean "480 lines of picture". I found something [http://www.alienbill.com/2600/101/02breach.html here] which gives us the following numbers (this is for programming those old Atari 2600s):
I've searched, but I've only found news regarding Plextor GigaRec writers (which do what I remember, but aren't the ones I read about years ago).
Could someone, knowing|finding, write a paragraph about this? ::I don't think such a thing exists. There are ways to burn a little more information, but a 45% increase...no. Unless you play the games marketeers played in the mid 90s where a given data tape would hold "750 megabytes" of data but only really stored 250 megabytes of uncompressed data. User:Samboy 03:16, 30 Mar 2005 (UTC) ==History== I have a problem with the intro to this section: "The Compact Disc is not an invention: it is the convergence of a series of enabling technologies, such as laser technology, mechanics, electronics, and coding technology. Therefore, nobody can claim that he or she is the inventor of the Compact Disc." The same sort of argument could be made for just about any invention. Take the automobile - we couldn't have cars if someone hadn't invented the wheel, wagons, metalurgy, internal combustion engines, etc. And of course we never would have CDs if nobody had invented lasers, transistors, computers, digital audio formats, etc. But just because an invention builds on previous inventions doesn't mean that it's any less an invention in its own right. Credit for the invention should be given to Philips and Sony and their "joint taskforce of engineers." --User:4.245.5.118 23:05, 25 Apr 2005 (UTC) Thank you for starting this discussion. I find it very interesting, but also extremely difficult, as one has to answer existential questions such as what is the Compact Disc? Is it just a digital version of the Videodisc developed in the 60s and 70s? What are the additional inventive steps? Taking 44.1 kHz as sampling frequency used in the prior art PCM adaptor? Is that a creative step? (': In the (patent) literature one can find optical audio recorders/players developed in the 1930s. Of course the technology was analog as PCM was invented in 1937. Those machines could not be mass produced as the key components were not available. In the 1960s, pioneering experiments with optical recording have been made when the gas laser became available. Digital audio and video optical recording became feasible for the consumer market after the invention and mass production of the solid-state laser and notably low-cost electronics. The ideas of optical recording have been around for a very long time, but could not be implemented in mass quantities without those key components. This is in sharp contrast with, for example, Edison's audio cylinder and Berliner's gramophone. The low-tech key components, wax, needle, and mechanics, were already available in the 16th century or earlier, but nobody came with the idea for the gramophone, or may be nobody had interest in it. There is, I think, no doubt that there was a Sony/Philips task force of about eight top engineers who made the required choices and trade-offs based on joint experiments and discussions. I agree that those, mostly anonimous, engineers should receive more credit for doing an excellent job around 25 years ago. I suggest that we delete the first sentence of the CD history section regarding the inventorship, and add the names of prominent members of the task force, such as Dr Toshi Doi (Sony) and Kees Immink (Philips). ---- I agree: The first two sentences of the History section come off sounding prematurely argumentative and not neutral. As User:4.245.5.118 points out, applying the supplied logic everywhere would negate the vast majority of "inventions". I'm certain that plenty of people (but not all) would permit something that combines existing technologies in new, novel, and previously unforseen ways to be rightly called an "invention". Thus, the existing two sentences are simply one POV in an argument, so they should be either balanced or removed. --User:Ds13 16:42, 2005 Apr 30 (UTC) ---- The following paragraph is taken from the official Philips' history web site www.research.philips.com/newscenter/dossier/optrec/index.html \begin{quote} Almost every week Philips receives a request for an interview with the inventor of the CD. That would undoubtedly make an interesting story. How do you put the gramophone record out of date in such a short space of time? And had the inventor already envisaged subsequent developments like the CD-ROM and the DVD? Unfortunately, the inventor of the CD does not exist. Nobody even invented one part of the technology alone. The CD was invented collectively by a large group of people working as a team. Emil Berliner, the founder of Deutsche Grammophon, might have been able to invent the gramophone record on his own in 1887, but the technology on which the CD is based is too complex for just one genius. \end{quote} So the 'official' Philips' POV is that the CD is not invented. Or even 'Nobody even invented one part of the technology alone'. Why do they want the world to believe that? ==Durability or longevity of the CD medium== I think it would be appropriate to add a longevity/lifespan/durability section in the article. With so much expensive audio and other data stored on CDs, it has become more common to discuss how long the data is expected to last and what can be done, if anything, to preserve or minimize degradation and/or to recover data from an aging CD. I'm no expert (thus, I'm on the talk page!), but related topics might be: * lifespan under ideal circumstances * normal wear and tear * damage ==Adding a link? == I found a CD-R FAQ, but before adding the link, should we advise the author? http://www.cdrfaq.org/ User:Eptalon :You don't need to notify the author. Also, that link should go on the CD-R page. - User:Mako098765''User_talk:Mako098765'' 07:20, 27 May 2005 (UTC)
See other meanings of words starting from letter:
Words begining with Compact_disc:
Compact_Disc
Compact_disc
Compact_disc
Compact_discs
Compact_Disc_Digital_Audio
Compact_disc_player
Compact_disc_player
Compact_Disc_Rewritable
Compact Disc
#REDIRECT Compact disc
Compact disc
A compact disc (or CD) is an optical disc used to store digital data, originally developed for storing digital audio. A standard compact disc, often known as an ''audio CD'' to differentiate it from later variants, stores audio data in a format compliant with the Red Book (audio CD standard) standard. An audio CD consists of several stereo tracks stored using 16-bit Pulse-code modulation coding at a sampling rate of 44.1 kHz. Standard compact discs have a diameter of 120mm, though 80mm versions exist in circular and "business-card" forms. The 120mm discs can hold 74 minutes of audio, and versions holding 80 or even 90 minutes have been introduced. The 80mm discs are used as "CD-singles" or novelty "business-card CDs". They hold about 20 minutes of audio. Compact disc technology was later adapted for use as a data storage device, known as a CD-ROM. == History == In the early 1970s, using video Laserdisc technology, Philips' researchers started experiments with 'audio-only' optical discs, initially with wideband frequency modulation FM and later digitized Pulse-code modulation audio signals. At the end of the 70s, Philips, Sony, and other companies presented prototypes of digital audio discs. In 1979 Philips and Sony decided to join forces, setting up a joint taskforce of engineers whose mission it was to design the new digital audio disc. Prominent members of the taskforce were Kees A. Schouhamer Immink and Toshi Doi. After a year of experiment and discussion the taskforce produced the 'Red Book (audio CD standard)', the Compact Disc standard. Philips contributed the general manufacturing process, based on the (unsuccessful) video Laserdisc technology. Philips also contributed the Eight-to-Fourteen Modulation, EFM, which offers both a large playing time and a high resilience against disc handling damage such as scratches and fingerprints; while Sony contributed the error-correction method, CIRC. The [http://www.exp-math.uni-essen.de/~immink/pdf/cdstory.pdf Compact Disc Story,] told by a former member of the taskforce, gives background information on the many technical decisions made, including the choice of the sampling frequency, playing time, and disc diameter. According to Philips, the Compact Disc was thus "invented collectively by a large group of people working as a team."[http://www.research.philips.com/newscenter/dossier/optrec/index.html] The Compact Disc reached the market in 1983, and this event is often seen as the 'Big Bang' of the digital audio revolution. The new audio disc was enthusiastically received and its handling quality received particular praise. From its origins as a music format, Compact Disc has grown to encompass other applications. Two years later, in 1985, the CD-ROM (read-only memory) was introduced. With this it was now possible to disseminate massive amounts of computer data instead of digital sound. A user-recordable CD for data storage, CD-R, was introduced in the early 1990s, and it became the de facto standard for exchange and archiving of computer data and music. The CD and its later extensions have been extremely successful: in 2004 the annual worldwide sales of CD-Audio, CD-ROM, and CD-R reached about 30 billion discs. == Physical details == Compact discs are made from a 1.2 millimetre thick disc of polycarbonate plastic coated with a much thinner layer of Super Purity Aluminium Aluminium (originally gold, which is sometimes still used for its data longevity) layer which is protected by a film of lacquer. The lacquer can be printed with a label. Common printing methods for compact discs are silkscreening and offset printing. CDs are available in two sizes. By far the most common is 120 mm in diameter, with a 74 minute audio capacity and a 650 MB data (See #Storage capacity). They are also available as 80 mm discs, a format which is mainly used for audio CD singles in some regions (like Japan), much like the old single (music). Each such "miniCD" or "Maxi CD" can hold 21 minutes of music, or 180 MB of data. There is 15 mm hole in the centre of the disc, usually used by a some form of clamp or clip device within the player to hold it in place and allow it to be rotated by a motor. The information on a standard CD is encoded as a spiral track of ''pits'' moulded into the top of the polycarbonate layer (The areas between pits are known as ''lands''). Each pit is approximately 125 nanometre deep by 500 nm wide, and varies from 850 nm to 3.5 micrometre long. The spacing between the tracks is 1.6 μm. To grasp the scale of the pits and land of a CD, if the disc is enlarged to the size of a stadium, a pit would be approximately the size of a grain of sand. The spiral begins at the center of the disc and proceeds outwards to the edge, which allows the different size formats available. A CD is read by focusing a 780 nm wavelength semiconductor laser through the bottom of the polycarbonate layer. The difference in height between pits and lands is one quarter of the wavelength of the laser light, leading to a half-wavelength phase difference between the light reflected from a pit and from its surrounding land. The destructive interference this reduces the intensity of the reflected light compared to when the laser is focused on just a land. By measuring this intensity with a photodiode, one is able to read the data from the disc. The pits and lands themselves do not represent the zeroes and ones of binary data. Instead a change from pit to land or land to pit indicates a one, while no change indicates a zero. This in turn is decoded by reversing the Eight-to-Fourteen Modulation used in mastering the disc, finally revealing the raw data stored on the disc. == Audio format == The format of the audio disc, known as the 'Red Book (audio CD standard)' standard, was laid out by SONY and Philips in 1981. Philips is responsible for the licensing program of the intellectual property pertinent to the Compact Disc including the 'CDDA' logo that appears on the disc. In broad terms the format is a two-channel (four-channel sound is an allowed option within the Red Book format) stereo 16-bit Pulse-code modulation encoding at a 44.1 kHz sampling rate. Reed-Solomon error correction allows the CD to be scratched to a certain degree and still be played back. The sampling rate of 44.1 kHz is inherited from a method of converting digital audio into an analog video signal for storage on video tape, which was the most affordable way to store it at the time the CD specification was being developed. A device that turns an analog audio signal into PCM audio, which in turn is changed into an analog video signal is called a PCM adaptor. This technology could store 6 samples (3 samples per each stereo channel) in a single horizontal line. A standard NTSC video signal has 245 usable lines per field, and 59.94 fields a second, which works out at 44,056 samples/second. Similarly PAL has 294 lines and 50 fields, which gives 44,100 samples/second. This system could either store 14-bit samples with some error correction, or 16-bit samples with almost no error correction. There was a long debate over whether to use 14 or 16 bit samples and/or 44.056 k or 44.1 k samples/s when the Sony/Philips taskforce designed the compact disc; 16 bits and 44.1 k samples/s prevailed. The Sony PCM-1610 and PCM-1630 are well-known examples of PCM-adaptors used in conjunction with the Sony U-Matic VCR. === Storage capacity === The main parameters of the CD (taken from the September 1983 issue of the Red Book (audio CD standard)) are as follows: *Scanning velocity: 1.2-1.4 m/s (constant linear velocity). *Track pitch: 1.6 μm. *Disc diameter 120 mm. *Disc thickness: 1.2 mm. *Inner radius program area: 25 mm. *Outer radius program area: 58 mm. We find that the program area equals 86.05 square cm, so that the length of the recordable spiral is 86.05/1.6 = 5.38 km. Given a scanning speed of 1.2 m/s, we note that the playing time is 74 minutes, or around 650 MB of data on a CD-ROM. In case the disc diameter would have been 115 mm, the maximum playing time would have been 68 minutes, i.e., 6 minutes less. A disc with data appearing slightly more densely is allowable. Using a linear velocity of 1.2 m/s and a track pitch of 1.5 micrometre leads to a playing time of 80 minutes, or a capacity of 700 MB. This is the limit for most conventional audio CDs today. Another technique to increase the capacity of a disc is store data in the lead out groove that is normally used to indicate the end of a disk, and an extra minute or two of recording is often possible. However, these discs can cause problems in playback when the end of the disc is reached. === Subcode === Besides digital audio, a CD contains digital data called 'subcode', which is multiplexed with the digital audio. The data in a CD is arranged in frames. A frame comprises 33 bytes, of which 24 are audio bytes (six full stereo samples), eight error correction, CIRC-generated, bytes plus one subcode byte. The eight bits of a subcode byte are available for control and display. The eight bits are used as eight different subcoding channels, and given letters designating their usage: P, Q, ..., W. Thus each channel has a bit rate of 7.35 (=44.1/6) kbit/s. In each sector there are 2352 bytes (24 * 98) of audio content data and 96 bytes of subchannel data. The 96 bytes of subchannel information in each sector contain four packets of 24 bytes apiece : 1 byte for command, 1 byte for instruction, 2 bytes for parityQ, 16 bytes for data, and 4 bytes parityP. Each of the 96 subchannel data bytes can be thought of as being divided into 8 bits. Each of these bits corresponds to a separate stream of information. These streams are called "channels", and are labeled starting with the letter P, like so: {| cellpadding=3 |- |Channel |P |Q |R |S |T |U |V |W |- |Bit |7 |6 |5 |4 |3 |2 |1 |0 |} Channel P is a simple pause/music flag, which can be used for low-cost search systems. Quite a few players ignore it in favor of the Q Channel. Channel Q is used for control purposes of more sophisticated players. It contains positioning information, the Media Catalog Number, and International Standard Recording Code. The ISRC is used by the media industry, and contains information about the country of origin, the year of publication, owner of the rights, as well as a serial number, and some additional tags: ;Data: This track contains Data (rather than audio). Can be used for muting in audio CD Players. ;Copy Flag: Used by the Serial Copy Management System to indicate permission to digitally copy the track. ;Four Channel Compact Disc Digital Audio: The track uses four channel audio. This is very rarely used on Compact Discs. ;Pre-Emphasis: The audio track was recorded with pre-emphasis. Used very rarely on Compact Discs. Channels R..W are unused by red-book compliant CDs, and have been used for extensions to the standard. === CD-Text === CD-Text is an extension of the Red_Book_(audio_CD_standard) standard for audio CDs. It allows to store additional information (like album name, song name, artist,..) on a standards-compilant audio CD. The information is stored in the lead-in area of the CD (there's roughly 5 Kilobytes space there), or in the Subchannels R to W on the disc, which are not used on red-book compliant CDs. About 31 Megabytes of information can be stored there. The text is stored in a format usable by the Interactive Text Transmission System (ITTS). ITTS is also used by Digital Audio Broadcasting or the MiniDisc. Please note that other extensions like CD+G also use those subchannels to store graphics in. == The AAD, ADD, DDD code for audio CDs == Originally, audio-format CDs came with a three letter code on the back, where "A" stood for analog signal and "D" stood for digital. The first letter represented how the album had been recorded, the second how it had been mixed, and the third how it had been transferred. As a result, almost all early CDs are "AAD" (analog recording and mixing, digital transfer to CD). Often this code was accompanied by a short description such as "Full Digital Recording" for DDD and "Digitally Mixed Analog Recording" for ADD. Although experimental recordings exist from the 1960s, digital recording of classical and jazz music began to be made commercially in the early 1970s, pioneered by Japanese companies such as Denon; the first 16-bit PCM recording in the United States was made at the Santa Fe Opera in 1976 on a Soundstream recorder. In most such cases, there was no mixing stage involved; a stereo digital recording was made and used unaltered as the master tape for subsequent commercial release. These, and other subsequent unmixed digital recordings are still described as DDD, as the technology involved is purely digital. (Likewise, unmixed analog recordings are usually described as ADD, to denote a single generation of analog recording). The first digitally recorded and mixed (DDD) popular music album was ''Bop Till You Drop'' by Ry Cooder in 1978. Many other top recording artists, such as Stevie Wonder, were early adherents of digital recording. Others, such as former Beatles producer George Martin, felt that the multitrack digital recording technology of early 1980s had not reached the sophistication of analog systems; however, he used digital mixing to eliminate the distortion and noise that an analog master tape would introduce (thus ADD). An early example of an analog recording that was digitally mixed is ''Tusk (album)'' by Fleetwood Mac, from 1979. By the time the compact disc was introduced worldwide, digital recording and mixing was becoming commonplace among recording artists and producers known for their interest in fidelity. Two examples from 1982 are ''Signals (album)'' by Rush, and ''The Nightfly'' by Donald Fagen. A few examples of DAD recordings exist, mostly of tunes that were originally recorded digitally but later remixed by artists who preferred to work with analog technology. When it started making LPs and cassettes, the originally CD-only label Ryko extended this system to the other media, so that a digital recording on an LP would be DDA, and so forth. == CD-ROM == For its first few years of existence, the compact disc was purely an audio format. However, in 1985 Yellow Book (CD-ROM_standards) CD-ROM standard was established by Sony and Philips, which defined a non-volatile optical data computer storage medium using the same physical format as audio compact discs, readable by a computer with a CD-ROM drive. The smallest entity in the CD audio format is called a ''frame''. A frame can accommodate six complete 16-bit stereo samples, i.e. 2*2*6 = 24 bytes. Data in a CD-ROM are organized in both frames and sectors. A CD-ROM ''sector'' contains 98 frames, and holds 98*24 = 2352 bytes. The CD-ROM is in essence a data disc, which cannot rely on error concealment, and it requires therefore a higher reliability of the retrieved data. In order to achieve improved error correction and detection, a CD-ROM has a third layer of Reed-Solomon error correction. Note that the CIRC error correction system used in the CD audio format has two interleaved layers. A Mode-I CD-ROM, which has the full third layer error correction capability, contains a net 2048 bytes of the available 2352 per sector. In a Mode-2 CD-ROM, which is mostly used for video files, we have 2336 user-available bytes per sector. The net byte rate of a Mode-1 CD-ROM is 44.1*2048/(6*98) = 153.6 byte/s. The playing time is 74 minutes, or 4440 seconds, so that the net capacity of a Mode-I CD-ROM equals 682 Mbyte. == Recordability == Injection moulding is used to mass produce compact discs. A 'stamper' is made from the original media (audio tape, data disc, etc.) by writing to a glass disc (referred to as a glass master) coated with a photosensitive dye with a laser. This dye is then etched, leaving the data track. It is then plated to make a positive version of the CD. Polycarbonate is liquified and injected into the mold cavity where the stamper transfers the pattern of pits and lands to the polycarbonate disc. The disc is then metallized with aluminum and lacquer coated. Recordable compact discs are injection molded with a "blank" data spiral. A photosensitive dye is then applied, and then the discs are metallized and lacquer coated. The write laser of the CD recorder changes the characteristics of the dye to allow the read laser of a standard CD player to see the data as it would an injection molded compact disc. CD-R recordings are permanent. The resulting discs can be read by most CD-ROM drives and played in most audio CD players. CD-RW is a re-recordable medium that uses a metallic alloy instead of a dye. The write laser in this case is used to heat and alter the chemical properties of the alloy and hence change its reflectivity. A CD-RW does not have as great a difference in the reflectivity of lands and bumps as a pressed CD or a CD-R, but many CD audio players cannot read CD-RW discs, although the majority of standalone DVD players can. == Copy protection == The Red Book audio specification does not include any copy prevention mechanism. ''Ripping'' is the process by which the contents of an audio disc is copied out verbatim to a duplicate disc or re-encoded into some other format, such as MP3. An CIRC is included with Red Book audio to deal with small scratches or defects on the disc media. Where error correction fails on larger defects, audio CD players are expected to apply interpolation algorithms to conceal the loss of audio data. Starting in early 2002, attempts were made by record companies to market "copy-protected" compact discs. Some of these deliberately introduced error patterns into audio tracks severe enough to defeat the error-correcting code (and hence defeat most CD-ROM drives attempting to copy the tracks as data), but not so disruptive as to prevent interpolation from working (hence allowing the same tracks to be played in audio mode without overly affecting high fidelity). Another copy protection method places a data track (usually containing bonus software for computer users) at the end of the disc and gives it an invalid size in the disc's table of contents. This is intended to prevent the data track from ripped, but can be defeated by ignoring the table of contents and reading the disc sector by sector. Philips has stated that such discs are not permitted to bear the trademarked ''Compact Disc Digital Audio'' logo because they violate the Red Book specification. It also seems likely that Philips' new models of CD recorders will be designed to be able to record from these 'protected' discs. However, there has been great public outcry over copy-protected discs because many see it as a threat to fair use. Other systems developed are Macrovision CDS-200 and Mediamax CD-3. In any case, even if a disc cannot be directly ripped, it can still be played in audio mode, and the audio thence captured. Any loss of sound quality caused by this method is generally considered negligible. This is commonly referred to as the analog hole. == Non-standard CD behaviors == Some commercially-released audio discs have a "secret" hidden track. These may be an extension of the last audio track or a separate track hidden from the disc's table of contents. Either way, the hidden portion is heard when the disc is played to the end. One such track is "Her Majesty (song)", a bonus track included on The Beatles' ''Abbey Road (album)'' album disc. It starts after 20 seconds of total silence after the final listed track, "The End (The Beatles song)". Other discs hide the extra material at the beginning of the disc. On most discs, the location of the first track listed in the table of contents immediately follows the table of contents itself. In this case, the hidden track is an unlisted track sandwiched between the two. To hear the hidden track, the listener must usually "rewind" the player past the beginning of the first listed track. Not all players allow this. == Name == Notwithstanding the variability of general usage between disk or disc [http://www.bartleby.com/61/16/C0521600.html], the customary spelling is "compact disc", rather than "compact disk". This may be in large degree due to its status as a Philips trademark under that spelling. == References == * Kenneth C. Pohlmann (1992). ''The Compact Disc Handbook''. Middleton, Wisconsin: A-R Editions. ISBN 895793008. == See also == * CD-ROM * CD-R * CD-RW * Rainbow Books ** Red Book (audio CD standard) ** Yellow Book (CD-ROM standards) * CD-G * Enhanced CD * Video CD * SVCD * Jewel case * CD Wallet * CD Organizer * Digipak * miniCD * Optical disc ** DVD CD 120 mm discs Audio storage Video storage als:Compact Disc fa:لوح فشرده ga:Dlúthdhiosca simple:Compact disc
Compact disc
I hope to see the 1X unit of CD throughput defined here some day, also the 1X of DVD defined there. I'm guessing the [http://www.google.com/search?q=define:+1X "Google define: 1X"] claims of 1X CD = 150,000 byte/s and 1X DVD = 1,380,000 byte/s are slightly incorrect, because seemingly imprecise, because rounded decimally. (Pat LaVarre, 21st September 2004) ::CD audio has 176,400 bytes a second of data to be precise (44100 * 2 bytes (16 bits) * 2 channels (stereo)). The error correction overhead for a data CD is roughly 13% (derived by the number of bytes of data an 80 minute CD fits compared to the number of bytes of audio data if burned as an audio CD), so we get 153,333 bytes a second. User:Samboy 02:03, 10 Nov 2004 (UTC) ::CD (according to the article) can hold 650 MB or 74 minutes. So assuming that a cd drive can read 650 MB in 74 minutes at 1x, the 1x read speed of a 650MB data CD is 650MB / 74 min = 650MB / (74 x 60 sec.) = 146,396 B/s = 1.17 Mbit/s. If by MB the article was referring to 1024 KB (the article is unclear on this!), then multiplying by 1.024 x 1.024, the modified figures are 153,508 B/s = 1.23 Mbit/s. --User:Tokek 03:58, 29 Mar 2005 (UTC) :::650MB is the capacity for data mode, which has more redundancy than audio mode. VCDs and audio CDs are written without the added redundancy, and have a max size of about 735MB on a "650MB" CD. So on a data CD, you're actually reading in the redundancy data along with the user data, which creates the 13% of overhead in Samboy's derivation. (I believe MB in this case does refer to the powers of two variety. Are we ever going to start using "Mebibyte"?) - User:Mako098765 01:05, 30 Mar 2005 (UTC) ::::Right, audio is (176,400 B/s) * (74mins) = 783,216,000 B, data is 650 MiB = 681,574,400 B, data read speed is (176,400 B/s) * (681,574,400 B / 783,216,000 B) = 153,508 B/s = 1.228 Mbit/s. Different calculations (both took overhead into account btw), same results. --User:Tokek 07:16, 30 Mar 2005 (UTC) :::::I just wanted to point out that the CD drive reads in the same amount of raw data at 1x for audio as well as data. Perhaps the article could benefit from an overview of effective sector sizes in different data modes. - User:Mako098765 21:13, 30 Mar 2005 (UTC) ::::::Good work, but all this probably belongs on the CD-ROM page. --User:Dtcdthingy 00:40, 31 Mar 2005 (UTC) ---- ''A 120mm disc can store about 74 minutes of music or about 650 megabytes of data.'' :Is it true that 74 minutes length was decided to have enough room for Beethoven's 9th symphony? I couldn't find any definitive reference. ::Yes. The president of Sony at the time (some Japanenese guy whose name eludes me at the moment) was a huge Beethoven fan. He wanted the compact disc to be big enough to hold Beethoven's 9th symphony its entirety (so that he wouldn't have to change the disc), so he basically demanded that the engineers make it hold 74 minutes. User:Raul654 03:23, Jul 1, 2004 (UTC) :::There is a lot of urban legends about this entire thing, so I will point people to [http://www.snopes.com/music/media/cdlength.htm this page]. The general impression I get is that, yes, the length of Beethoven's 9th did increase the diameter by one centimeter so that a CD could fit all fo the 9th (which usually doesn't need 74 minutes, but needs more than 60 minutes, which is how much time we would have gotten if we didn't increase the diameter by a centimeter). User:Samboy 01:57, 10 Nov 2004 (UTC) ---- In my opinion, the discussion about disc vs. disk is a moot point because "compact disc" is a tradename not a generic name. What is with the disc vs. disk anyway? I have always used disk for a disk and disc when referring to something round. My spell checker seems to say that they can be both used for a tech disk though, odd. --User:Josquius 16:58, 20 May 2004 (UTC) You're right - despite what any dictionary says, the inventors of teh compact disc named it disc. It's a brand name. You don't accept "cleanex" as a correct spelling for "Kleenex", or "zerocks" for "Xerox". Disc it is disc it always has been, and disc it always shall be. Don't believe me, go look at the logo. It's on every CD jewel case. History, please! When was the CD created, 1983? CD-R, early 1990s? And the CD-RW? And how about a link to a more generic entry on data storage? Further, how did the engineers decide on the diameter? Was it to match the 5.25" floppy disks common in the early 1980s? Or was it to have enough room for an hour of music or for Beethoven's 9th Symphony? The CD was created in 1979. It was introduced to the U.S. in 1982. The first CD recorder was made by Yamaha and imported to the U.S. in 1988 (I was working for the company that imported it). CD-RW didn't come into being until about 1996. :The Philips trademark may spell it "disc", but that's not itself definitive as to general usage. The current article text is needlessly prescriptive; newspaper style guides are poor sources on such matters, since their purpose is internal consistency, not to determine the "only correct usage". If a section like this is even appropriate, better that it mention the trademark and the history, not seek to provide "usage notes" as the current text does. User:Alai 03:25, 20 Mar 2005 (UTC) :: It goes to show that some people consider the correct spelling to be very important. And from what I've seen, it's always been disc with a "c". I do agree that quoting the entire style guide entry is unnecessary; a small mention is sufficient. - User:Mako098765 08:26, 21 Mar 2005 (UTC) ---- The CD-ROM was pushed by Bill Gates? This needs a bit more info! - User:David Gerard 13:09, Jan 13, 2004 (UTC) : See Bill Gates User:Mikkalai 04:35, 27 Jan 2004 (UTC) ---- ''The advantage of MP3 is that it increases CD storage capacity by up to ten times without significant degradation in sound quality.'' That's likely to get an argument from some audiophiles! --User:Calieber 16:46, Feb 15, 2004 (UTC) ---- That intro is a tangled mess and not at all a good encapsulated summary of what a CD is and is for - the sort of thing that would make a useful concise article in itself. Anyone want to try a rewrite? - User:David Gerard 16:08, Mar 10, 2004 (UTC) ---- Hmm, the business-end of the CD is not depicted in a photo yet. User:Kim Bruning 14:09, 5 Apr 2004 (UTC) :I'm about to buy a digital camera ... mind you, I'll be on holiday with it for three weeks! Anyone? Anyone? - User:David Gerard 14:18, Apr 5, 2004 (UTC) ---- Interwiki rules: http://nl.wikipedia.org/wiki/Afbeelding:CompactDisc.jpg have a nice day :-) ---- ''For drives installed in computers, all current CD-ROM and DVD-ROM drives can read and write CD-R and CD-RW discs.'' This is nonsense. ''ALL'' is VERY false. Recordable drives are almost never called ROM drives. This implies that no more CD-ROM or DVD-ROM drives are made. Only CD-RW drives, DVD-ROM/CD-RW combo drives, Or DVD+/-R(W) (also DVD-ram) drives are made. Therefore I have removed this Statement from the main page. Feel free to correct it and place it back on the page. User:Tacvek 22:55, 15 Jun 2004 (UTC) I realize that CDs are constant linear velocity, but what are the general maximum and minimum speeds for reading at 1X (CD audio)? User:Ckape 22:46, 22 Sep 2004 (UTC) == sampling frequency == Explain why CDs have a sampling frequency of precisely 44.1KHz ::I have added the answer to the article: ::The reason why the unusual sampling rate of 44.1kHz was chosen was because, at the time the CD specification was being developed, the only way to make a reasonably affordable digital audio recorder was to convert digital audio in to a video signal, which was then recorded to a VCR. A NTSC video signal has 245 lines of resolution, updated 60 times a second; a PAL video signal has 294 lines of resolution, updated 50 lines a second. The technology could store 3 samples in a single horizontal line, either at 14 bits with some error correction, or at 16 bits with almost no error correction. There was a debate over whether to use 14 or 16 bit samples when they designed the compact disc; 16 bits prevailed. Hence, the decision to use the 16-bit, 44.1kHz sampling rate. The Sony PCM-1630, an early CD mastering machine, was just a modified U-Matic VCR User:Samboy 02:04, 10 Nov 2004 (UTC) :::Researching this a littlmore a raw NTSC signal has 525 lines of resolution, updated 30 times a second (the number is different above because of interlacing). Some of this signal is part of the vertical blank, but some of this signal is the invisible part used for storing closed captioning and what not. Everyone says that NTSC has 480 lines of visible resolution, but the people who made those old PCM encoders (mainly Sony) figured out some way to get another ten lines in there somehow. I can't find any details online, but I guess they used part of the signal made invisible for closed captioning purposes and what not. User:Samboy 13:39, 20 Dec 2004 (UTC) :::: The vertical sync signal between each field is quite complex, spread out over several lines. I presume 245 is the maximum number of lines that VCRs would reliably record; and that would leave enough room for a reasonably valid sync signal in between that would not confuse a VCR. :::: The 525 lines figure actually just means 1 line lasts 1/525th of 1/30th of a second, it doesn't account for blanking interval. I guess the 480 lines figure comes from digitizing NTSC video. :::: User:Dtcdthingy 19:53, 20 Dec 2004 (UTC) :::::I think the 480 line figure also comes from people being conservative about the number of scan lines in a NTSC signal that contain actual picture information. The people that say "480 lines" are usually making digital TVs and what not; they mean "480 lines of picture". I found something [http://www.alienbill.com/2600/101/02breach.html here] which gives us the following numbers (this is for programming those old Atari 2600s):
:::::Now, from this, I get the sense they could have maybe have gotten as many as as 259 lines from a single frame. They grabbed 245 lines; it may be that the rotary heads on the old U-Matic VCRs spun at a speed such that they didn't record during some of the V-Sync signal. The specs for these old VCRs publically released do not tell us how many scan lines they recorded in a second, alas. I looked over at [http://labguysworld.com this page] and the manuals only discuss horizontal resolution; the big number at the time was how much horizontal resolution you could get; people didn't even think twice about the vertical resolution. :::::If different numbers of scan lines were chosen, here is the sampling rates we would have had:* 192 visible lines * 30 "overscan" lines (presumably visible to a VCR, but not visible to some TVs) 222 lines so far. * 37 "vertical blank" lines. 259 lines so far. * 3 lines during the actual vertical sync. 262 lines total. 262 * 2 = 524; this is as close to the 525 number possible because of interlacing.
:::::Somebody in the 1970s decided that 245 lines in a single frame was the maximum number of scan lines they could safely use and we can only speculate about what factors they considered when making this decision. It's strange that something as universal as the 44.1kHz sampling rate is something whose origins we can't fully track down. And, oh, Merry Christmas! User:Samboy 12:52, 25 Dec 2004 (UTC) ::::I assume the "245 lines" thing is per ''field'' and not per ''frame''. PAL and NTSC are interlaced video, meaning only every other horizontal line is updated every 1/50 or 1/60 of a second. Nearly all PAL/NTSC-based video recording formats utilise all 480/525 or 576/625 lines per frame - with exceptions of VCD and some early home video tape format that skipped every other field for long-play recording (I forget what it was), nothing reduces the vertical resolution. Also, sometimes I hear NTSC being quoted as having 483 lines of visible video. --User:Zilog Jones 16:54, 18 Jun 2005 (UTC) == Size of center hole == THe size of the center hole of the CD is the dutch equivilent of the penny. Phillips developed it there and they needed a size for the center, so I guess that just used a coin. If anyone knows the coin name please add it. : Yes, it appears to be more or less the same size as a Dutch 10 cent coin, which appears to be exactly 15mm. --User:Zilog Jones 01:29, 13 Jun 2005 (UTC) ::Can it be comfirmed there is an actual relation between the two? I've added it to the article for now - previously there was no mention of the hole and its purpose at all so I said some stuff on that too. --User:Zilog Jones 17:57, 15 Jun 2005 (UTC) :The diameter of CD's center hole is irrelevant for Wikipedia. It has no effect on the playing time, capacity, or other key parameters of the CD and DVD. The possible relationship with the Dutch 10ct coin is coincidental. In the same way as you did, I could write that CD's outer diameter, 12 cm, is the same as that of the Heineken beermat (coaster). And as you may know, Philips and Heineken are Dutch companies! So my conclusion, let us stop listing (unproven) trivialties in wikipedia, so pls remove your contributions regarding the center hole and the Dutch coin. User:Dsc 14:31, 19 Jun 2005 (UTC) ::OK, similarities with the coin have been removed, but the mention of the hole being there is by no means irrelevant - especially in the "physical details" section. It is a vital part to the functioning of the disc. --User:Zilog Jones 20:58, 20 Jun 2005 (UTC) == Compact Disc Unique Number == does anyone know if there is a unique number that differs manufactured compact disks.. like a MAC adress in network devices.. and if this unique number or ID exists.. why it is not used for copy protection.. and if this number does'nt exists why manufacturers dont adding it to there product for them it will be a simple to create a CD with uniq ID that can't be flashed or overwritened... and for software,game or audio developers it will be more easy to protect there product.. To my knowledge there isn't. All there is that could be used is that the TOC of a pre-recorded disk looks different to that of a CD-R. :CD-ROMs are mass-produced, "stamped" out from aluminum "masters". That makes all of them identical. I suspect that CD-ROM manufacturers don't add unique serial numbers because * (a) Adding a unique serial number would definitely add cost. * (b) Adding a unique serial number ''might'' bring in slightly more income from people who otherwise wouldn't have paid for the CD. Or it ''might'' not make any difference. :In other words, I suspect that the CD-ROM manufacturers don't add unique serial number because they think the (hypothetical) benefits are worth the (all-too-real) cost. :On the other hand, I've been told that CD-R and CD-RW disks are tested by writing some data and making sure that data can be read without error. It wouldn't cost anything (just a one-time change to the test software) to add a unique number to each of those disks. ==Overburn== The external links to overburning information, while useful, aren't really relevant here. I'm going to move them to overburning and place a reference to that article in the Recordability section. - User:Mako098765 07:06, 2 Dec 2004 (UTC) == regarding 'other burning technology' for CD == I remember something regarding cd-writers able to burn ~1 GB of data in 700-MB CDs.* 240 ("480 lines" resolution): 43.2 kHz * 245: 44.1 KHz (this was the one chosen) * 250: 45 kHz * 255: 45.9 kHz * 259: 46.620 kHz (this would have been ''really'' pushing it)
I've searched, but I've only found news regarding Plextor GigaRec writers (which do what I remember, but aren't the ones I read about years ago).
Could someone, knowing|finding, write a paragraph about this? ::I don't think such a thing exists. There are ways to burn a little more information, but a 45% increase...no. Unless you play the games marketeers played in the mid 90s where a given data tape would hold "750 megabytes" of data but only really stored 250 megabytes of uncompressed data. User:Samboy 03:16, 30 Mar 2005 (UTC) ==History== I have a problem with the intro to this section: "The Compact Disc is not an invention: it is the convergence of a series of enabling technologies, such as laser technology, mechanics, electronics, and coding technology. Therefore, nobody can claim that he or she is the inventor of the Compact Disc." The same sort of argument could be made for just about any invention. Take the automobile - we couldn't have cars if someone hadn't invented the wheel, wagons, metalurgy, internal combustion engines, etc. And of course we never would have CDs if nobody had invented lasers, transistors, computers, digital audio formats, etc. But just because an invention builds on previous inventions doesn't mean that it's any less an invention in its own right. Credit for the invention should be given to Philips and Sony and their "joint taskforce of engineers." --User:4.245.5.118 23:05, 25 Apr 2005 (UTC) Thank you for starting this discussion. I find it very interesting, but also extremely difficult, as one has to answer existential questions such as what is the Compact Disc? Is it just a digital version of the Videodisc developed in the 60s and 70s? What are the additional inventive steps? Taking 44.1 kHz as sampling frequency used in the prior art PCM adaptor? Is that a creative step? (': In the (patent) literature one can find optical audio recorders/players developed in the 1930s. Of course the technology was analog as PCM was invented in 1937. Those machines could not be mass produced as the key components were not available. In the 1960s, pioneering experiments with optical recording have been made when the gas laser became available. Digital audio and video optical recording became feasible for the consumer market after the invention and mass production of the solid-state laser and notably low-cost electronics. The ideas of optical recording have been around for a very long time, but could not be implemented in mass quantities without those key components. This is in sharp contrast with, for example, Edison's audio cylinder and Berliner's gramophone. The low-tech key components, wax, needle, and mechanics, were already available in the 16th century or earlier, but nobody came with the idea for the gramophone, or may be nobody had interest in it. There is, I think, no doubt that there was a Sony/Philips task force of about eight top engineers who made the required choices and trade-offs based on joint experiments and discussions. I agree that those, mostly anonimous, engineers should receive more credit for doing an excellent job around 25 years ago. I suggest that we delete the first sentence of the CD history section regarding the inventorship, and add the names of prominent members of the task force, such as Dr Toshi Doi (Sony) and Kees Immink (Philips). ---- I agree: The first two sentences of the History section come off sounding prematurely argumentative and not neutral. As User:4.245.5.118 points out, applying the supplied logic everywhere would negate the vast majority of "inventions". I'm certain that plenty of people (but not all) would permit something that combines existing technologies in new, novel, and previously unforseen ways to be rightly called an "invention". Thus, the existing two sentences are simply one POV in an argument, so they should be either balanced or removed. --User:Ds13 16:42, 2005 Apr 30 (UTC) ---- The following paragraph is taken from the official Philips' history web site www.research.philips.com/newscenter/dossier/optrec/index.html \begin{quote} Almost every week Philips receives a request for an interview with the inventor of the CD. That would undoubtedly make an interesting story. How do you put the gramophone record out of date in such a short space of time? And had the inventor already envisaged subsequent developments like the CD-ROM and the DVD? Unfortunately, the inventor of the CD does not exist. Nobody even invented one part of the technology alone. The CD was invented collectively by a large group of people working as a team. Emil Berliner, the founder of Deutsche Grammophon, might have been able to invent the gramophone record on his own in 1887, but the technology on which the CD is based is too complex for just one genius. \end{quote} So the 'official' Philips' POV is that the CD is not invented. Or even 'Nobody even invented one part of the technology alone'. Why do they want the world to believe that? ==Durability or longevity of the CD medium== I think it would be appropriate to add a longevity/lifespan/durability section in the article. With so much expensive audio and other data stored on CDs, it has become more common to discuss how long the data is expected to last and what can be done, if anything, to preserve or minimize degradation and/or to recover data from an aging CD. I'm no expert (thus, I'm on the talk page!), but related topics might be: * lifespan under ideal circumstances * normal wear and tear * damage ==Adding a link? == I found a CD-R FAQ, but before adding the link, should we advise the author? http://www.cdrfaq.org/ User:Eptalon :You don't need to notify the author. Also, that link should go on the CD-R page. - User:Mako098765''User_talk:Mako098765'' 07:20, 27 May 2005 (UTC)
See other meanings of words starting from letter:
C
CA | CB | CD | CE | CF | CG | CH | CI | CJ | CK | CL | CM | CN | CO | CP | CR | CS | CT | CU | CW | CX | CY | CZ |Words begining with Compact_disc:
Compact_Disc
Compact_disc
Compact_disc
Compact_discs
Compact_Disc_Digital_Audio
Compact_disc_player
Compact_disc_player
Compact_Disc_Rewritable
Sponsored links: praca, nurkowanie.
These materials are based on Wikipedia and licensed under the GNU FDL
YouTube.com videos better site than Turbo Tax 2007
