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. The rest are not used in the Red Book specification. • '
Channel P'''
is a simple "pause music" flag, which can be used for low-cost search systems. Many players ignore it in favor of the Q'' Channel. It indicates a start of a new track by at least two consecutive seconds (150 sectors) of all 1s, and the last block with all 1s is the first block of the new track. • '
Channel Q''''' is used for control purposes of more sophisticated players. It has three different modes, but with a common structure for all of them. of the disc. •
Q Mode 3: In this mode, the data bits contain an
International Standard Recording Code (ISRC) for each track (applicable to CD-DA only). 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. •
Cyclic redundancy check bits: The last 16 bits contain an error detection code computed over the previous bits of the channel. • '
Channels R
through W''''' are unused by Red Book compliant CDs and Yellow Book compliant CD-ROMs, and have been used for extensions to the standard: •
CD-Text is an extension to the
Red Book standard for audio CDs. It allows for storage of additional information (e.g. album name, song name, and artist) on the
R through
W subcode channels on the disc (either in the lead-in area or in the program or main area). • The
CD+G or "karaoke" extension also uses the
R through
W subcode channels to store low resolution graphics. • Several
copy protection systems made use of the fact that some
disk copying utilities neglect to copy subcode data due to the obscurity of it.
CloneCD can read subcode data and save it to a
CloneCD Control File. ==Jack on CD players==