Compact Disc subcode

In addition to the pure user data and the parity bytes of CIRC a so-called subcode of information to read out the data by CD players while writing data to a CD (audio CD, CD -ROM, ...) is embedded, includes. Such data include, depending on the CD standard such as tables of contents, seasons, titles, trademarks, index markers, ISRC, text ( track titles, lyrics ), MIDI data, or even graphics.

On a CD 14 of 588 channel bits per frame, so 8/588 = 1.36% of the volume for the subcode reserved. Just one data byte per frame with 24 bytes of data payload, so 98 bytes per subcode sector. Each byte of this data stream is divided into eight different channels, which are designated by the uppercase letters P, Q, R, S, T, U, V and W. CD players simply ignore the channels that they do not support.

Subcode channels

  • P- channel: start mark a track ( P = 1 during the break between songs and P = 0 while the title).
  • Q- channel: Includes all information for controlling the playback operation: time information, both in absolute CD- beginning as well as relative to the start mark of the title, track number, index markers and ISRC; the lead-in area of ​​the Q- channel the table of contents ( TOC = Table Of Contents) contains (72 bits / sector)

Construction of Q channel

S0 S1 Bit - Bit control bits (4 ) Adr.Bits (4 ) data bits ( 72 ) CRC bits (16 )

- S0, S1 Bit: synchronization for the sub-code demodulation - Contr.Bits: pre-emphasis ( treble boost take-up side ); Number of audio channels ( 1 bit is the first bit in the data stream, and thus since the most significant bit in the nibble)    ~ Bit 1: 0 for 2 channel and 1 for 4 channels    ~ Bit 2: 1 for data tracks    ~ Bit 3: 0 for copy protection and allows for 1 Digital copy    ~ Bit 4: 0 for pre-emphasis off and 1 for a - Adr.Bits: a description of how data bits are to be interpreted    ~ Mod 1 (0001 ): Information about the number of pieces of music indexing and term    ~ Mod 2 (0010 ): indication of cataloging the CD    Mod ~ 3 (0011 ): identifier ( eg ISRC ) - CRC for error correction Channels RW: MIDI, sign graphics, CD -text data, ... ( CD Formats CD G and CD-Text )

Compact Disc Digital Audio CD-ROM International Standard Recording Code
753028
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