Control and Display signals

Also called PQ codes. In the CD format, eight additional bits are added to each frame of audio data; this means that a byte of information is available from the disc every 136 µs. Each bit in the added byte is given a one-letter name, P-W. Thus, eight separate subcodes can be recorded on and recovered from the CD. So far only P and Q are used: the P-code is used for the pause signal between musical tracks and at the end of the last track, and the Q-code tells the player if the recording is two- or four-channel (no quadraphonic CD player is yet available). The Q-code also contains timing information about the tracks and identifies the country of origin and date of the recording. No standard has been defined for the use of the other six subcodes.