CD-G

From Academic Kids

The title of this article is incorrect because of technical limitations. The correct title is CD+G.

A CD+G 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).

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.

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 Managment System to indicate permission to digially 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 videogame consoles Sega CD, Sega Saturn, and the Atari Jaguar CD (which was an attachment to the Atari Jaguar) also played CD+G format CDs.

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.

Discography of CD+Gs

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