A CD+G (also known as CD+Graphics) is a special audio compact disc that contains graphics data in 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, can output a graphics signal (typically, the CD+G player is hooked up to a television set or a computer monitor); these graphics are almost exclusively used to display lyrics on a television set for karaoke performers to sing along with.

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:
Channel P Q R S T U V W
Bit 7 6 5 4 3 2 1 0

Both the P and Q channels on a regular audio CD are used for timing information. They are used to 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 CD-TEXT as well.

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 System to indicate permission to digitally copy the track.

Four-Channel 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 are used to store graphics information.

In the CD+G system, 16-color (4-bit) graphics are displayed on a raster field which is 300×216 pixels in size.

The following videogame consoles played CD+G format CD's: TurboGrafx CD (a CD-ROM peripheral for the TurboGrafx 16), Turbo Duo, Sega CD, 3D0, Sega Saturn, Commodore Amiga CD32 and the Atari Jaguar CD (which was an attachment to the Atari Jaguar).

CD+G has had a resurgence of late, and is being used for CDs for karaoke systems, with the graphics used to display song lyrics.

Wikipedia information about CD+G. This article is licensed under the GNU Free Documentation License . It uses material from the Wikipedia article 'CD+G'