Whats in a subcode channel?
There are 8 subcode channels, labeled P,Q,R,S,T,U,V,W, or sometimes “P-W” for short. (The ECMA-130 standard refers to subcode bytes as “Control bytes”.) Every frame contains one byte of subcode data, and each byte holds 1 bit of P, 1 of Q, and so on. The bytes from 98 consecutive frames are combined to form a subcode “section”. The first two bits in each channel are used for synchronization, leaving 96 bits of useful data per channel (which is where RAW DAO-96 gets its name). The P and Q channels are defined by the CD audio standard. (They are unrelated to the P and Q parity fields.) The P channel can be used to find the start of a track, but in practice most devices use the more sophisticated Q channel. Q contains four chunks of information: control (4 bits), address (4 bits), Q data (72 bits), and an EDC (16-bit CRC). The control bits determine whether the track holds audio or data, the number of audio channels (stereo or quadraphonic), and specifies the Digital Copy Permitted and Pr
(2002/12/11) There are 8 subcode channels, labeled P,Q,R,S,T,U,V,W, or sometimes “P-W” for short. (The ECMA-130 standard refers to subcode bytes as “Control bytes”.) Every frame contains one byte of subcode data, and each byte holds 1 bit of P, 1 of Q, and so on. The bytes from 98 consecutive frames are combined to form a subcode “section”. The first two bits in each channel are used for synchronization, leaving 96 bits of useful data per channel (which is where RAW DAO-96 gets its name). The P and Q channels are defined by the CD audio standard. (They are unrelated to the P and Q parity fields.) The P channel can be used to find the start of a track, but in practice most devices use the more sophisticated Q channel. Q contains four chunks of information: control (4 bits), address (4 bits), Q data (72 bits), and an EDC (16-bit CRC). The control bits determine whether the track holds audio or data, the number of audio channels (stereo or quadraphonic), and specifies the Digital Copy Per
(2002/12/11) 98 frames of 24 bytes are combined to form a 2352-byte sector and 98 bytes of subcode data. The sector is assembled from F1 Frames, which are byte-swapped, shuffled, and run through a descrambler. The purpose of the scrambler is to reduce the likelihood that regular bit patterns will induce a large digital sum value. It should be pointed out that the 2352-byte sector is the smallest unit most CD-ROM drives will allow software to manipulate. It’s only after all of the above that low-level CD-ROM operations, like “RAW DAO-96” reads and writes, begin. This is why making a “bit-for-bit” copy of a disc is tricky. A sector on an audio CD holds 2352 bytes of data. 16-bit stereo samples require 4 bytes per sample, so there’s 2352/4 = 588 samples per sector. At 75 sectors per second, that’s 44100 samples per second (44.1KHz). At this point, the processing for an audio CD is essentially complete. CD players feed the samples through a DAC (or S/PDIF connector) and eventually out to t
