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

recordings contain two channels of 44.1-kHz 16-bit linear PCM audio. However, creators of the CD originally contemplated a four-channel, or

quadraphonic Quadraphonic (or quadrophonic and sometimes quadrasonic) sound – equivalent to what is now called 4.0 surround sound – uses four audio channels in which speakers are positioned at the four corners of a listening space. The system allows for th ...

, mode as well. The proprietary Red Book specification, as published by

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

and

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

, briefly mentions a four-channel mode in its June 1980,"Red Book" Audio CD specification, June 1980, Sony/Philips September 1983,"Red Book" Audio CD specification, September 1983, Sony/Philips and November 1991"Red Book" Audio CD specification, November 1991, Sony/Philips editions. On the first page, it lays out the "Main parameters" of the CD system, including: "Number of channels: 2 and/or 4 simultaneously sampled." The footnote says, "In the case of more than two channels the encoder and decoder diagrams have to be adapted." The Red Book also reserved the first bit of the so-called Q subchannel "control field" to signal the presence of four-channel audio, but did not specify a method for using four-channel in the CD system. Had it been later specified, this mode might have included four separate channels of linear PCM audio (requiring some combination of faster rotation, a lower sampling rate, fewer bits per sample, or compression). Alternatively, the "four-channel" bit could have been used merely to indicate the presence of a

matrix Matrix most commonly refers to: * ''The Matrix'' (franchise), an American media franchise ** ''The Matrix'', a 1999 science-fiction action film ** "The Matrix", a fictional setting, a virtual reality environment, within ''The Matrix'' (franchis ...

-encoded recording, for example

Dolby Pro Logic Dolby Pro Logic is a surround sound processing technology developed by Dolby Laboratories, designed to decode soundtracks encoded with Dolby Surround. Dolby Stereo (also known as ''Dolby MP'' or ''Dolby SVA'') was developed by Dolby in 1976 ...

. In reality, however, the underspecified "four-channel" mode was dropped from the CD standard when it was adopted by the

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

and became IEC 908:1987, and later IEC 60908:1999. (Various national authorities have also adopted the IEC standard. E.g., it is also European Standard EN 60908:1999.) Neither the 1987 nor the 1999 version of the IEC standard discusses the possibility of four-channel audio. Instead, the IEC document reserves the first bit of the Q subchannel "control field" to a different, although similarly cryptic, purpose—according to clause 17.5 note 2, it is for "Broadcasting use" in "non-audio applications of the Compact Disc." Since the behavior of the "four-channel" or "Broadcasting use" bit was never specified by either CD standard, no mass-marketed discs have attempted to use the Red Book's four-channel mode, and no players have purported to implement it.

References

External links

Apple discourages use of four-channel flag
{{Compact disc Audio storage Compact disc Japanese inventions Quadraphonic sound

See also

References

External links