CD+G
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| Media type | Optical disc |
|---|---|
| Encoding | Various |
| Capacity | Typically up to 700 MB (up to 80 minutes audio) |
| Read mechanism | 780 nm wavelength semiconductor laser |
| Developed by | Philips & Sony |
| Usage | Audio, image, and data storage |
| Optical media types | |
|---|---|
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| Standards | |
| Further reading | |
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CD+G (also known as CD+Graphics) is an extension of the compact disc standard which can present low-resolution graphics alongside the audio data on the disc when played on a compatible device. CD+G discs are often used for karaoke machines, which utilize this functionality to present on-screen lyrics for the song contained on the disc.
Along with dedicated Karaoke machines, other consumer devices that play CD+G format CDs include the NEC TurboGrafx-CD (a CD-ROM peripheral for the TurboGrafx-16) and Turbo Duo, the Philips CD-i, the Sega Saturn and Sega CD, the 3DO Interactive Multiplayer, the Commodore Amiga CD32 and CDTV, and the Atari Jaguar CD (which was an attachment for the Atari Jaguar). Some CD-ROM drives can also read this data. Since 2003, some standalone DVD players have supported the CD+G format. These include various Chinese-made brands sold in discount stores. The CD+G capability on these players is often unadvertised, and may not function correctly with all CD+G disks.
Implementation
In each sector there are 2352 bytes (24 * 98) of audio content data and 96 bytes of compact disc 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 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:
| 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 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 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 raster field which is 300×216 pixels in size.
See also
External links
- The CD+G Museum and Discography, details on released titles and how to identify them
- How to Rip a Karaoke CD A step by step guide to back up CDGs.
- CD+G revealed - The HTML version of the no longer available cdg_revealed.txt file
- CD+G faq
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