A CD+G (also known as CD+Graphics) is a special audio
compact discthat contains graphics datain addition to the audio data on the disc.The disc can be played on a regular audio CD player, but when played on a special CD+G player (such as the Sega Saturn), can output a graphics signal (typically, the CD+G player is connected to a televisionset or a computer monitor); these graphics are almost exclusively used to display lyricson a television set for karaokeperformers to sing along with.
In each sector there are 2352
bytes (24 * 98) of audio content data and 96 bytes of compact disc subcode.
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 parity Q,
*16 bytes for data, and
*4 bytes parity P.
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:
Both the P and Q channels on a regular audio CD are used for timing information. They assist the CD player in tracking the current location on the disc, and to provide the timing information for the time display on the CD player. Note that same space is used for
Channel Q is used for control purposes of more sophisticated players. It contains position information the Media Catalog Number (MCN), and International Standard Recording Code (ISRC). 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.
;SCMS flag: Used by the
Serial Copy Management Systemto indicate permission to digitally copy the track.
Four-channel compact disc digital audio: The track uses four channel audio. Used very rarely on Compact Discs.
;Pre-emphasis: The audio track was recorded with
pre-emphasis. Used very rarely on Compact Discs.
The CD+G format takes advantage of the channels R through W, which are unused in standard audio CD formats. These six bits store graphics information.
In the CD+G system, 16-color (4-bit) graphics are displayed on a
rasterfield which is 300×216 pixels in size.
Among the consumer devices that play CD+G format CDs are the NEC TurboGrafx-CD (a CD-ROM peripheral for the
TurboGrafx-16) and Turbo Duo, the Philips CD-i, the Sega Saturnand Sega CD, the 3DO Interactive Multiplayer, the Commodore Amiga CD32and CDTV, and the Atari Jaguar CD(which was an attachment for the Atari Jaguar).
CD+G has had a resurgence as of 2004, and is being used for CDs for
karaokesystems, with the graphics used to display song lyrics.
* [http://www.cdplusg.com/ The CD+G Museum and Discography, details on released titles and how to identify them]
* [http://www.opentutorial.com/Rip_a_karaoke_cd How to Rip a Karaoke CD] A step by step guide to back up CDGs.
* [http://www.jbum.com/cdg_revealed.html CD+G revealed - The HTML version of the no longer available cdg_revealed.txt file]
* [http://www.ncf.carleton.ca/~aa571/cdgfaq.htm CD+G faq]
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