All audio CDs have 8 channels of subcode data that are interleaved with the digital audio data. The channels are named P, Q, R, S,T, U, V and W. In audio CDs, only channels P and Q are used by the CD player. The information in the P channel tells the CD player when songs are playing and when they are not. The information in the Q channel is much more comprehensive, describing track and disc running times, copy protection and emphasis information, disc catalog code and song identification codes, etc.