User Manual

Information area
Within the information area are three primary areas: lead-in, program, and lead-out.
Lead-in area
The lead-in area comprises approximately the first two minutes on any compact disc and is generally unused for recording actual audio
data. The main purpose of this area is to store the table of contents (TOC), which keeps an account of each track's location on the disc.
The TOC is written to the lead-in area of the disc once all of the information has been recorded to the disc. Before the TOC is written, only
the recorder can access the disc. Once the TOC has been written to the disc, any CD player or drive can play the disc.
Program area
All audio data is generally contained within tracks in the program area. The program area on a standard CD can hold 74 minutes of
audio, corresponding to the 74-minute maximum playing time of a standard CD-DA (Compact Disc-Digital Audio) disc. A maximum of
99 audio tracks can be contained in the program area, with each track normally holding one song.
Note: The Red Book specification allows for a theoretical maximum of 80 minutes of audio data on a disc. However, 80-
minute CDs may not play correctly on all CD players.
Within each track on the compact disc, there are subdivided frames, 1/75th of a second in length and containing 2352 bytes. Each frame
consists of audio data, parity bits, the synchronization word, and an 8-bit field, called a control byte.
The control byte is then broken down into separate subchannels—P, Q, R, S, T, U, V, and W—where each bit represents a subcode
channel. All of these subchannel bits are used in the audio format.
Subcode channel P (first bit)
The P channel indicates what part of the disc is being read: lead-in, program, or lead-out. The P channel also indicates start times and
end times for each track on the disc.
Subcode channel Q (second bit)
Compact disc players use the Q channel to display the music playing time. The Q channel is broken down into three modes:
Mode Description
Mode 1 Contains the running times from both the beginning of the disc (total disc time) and the
beginning of the track (track relative time).
Mode 2 Identifies the track number, who recorded the track, where it was recorded, and in what year.
Mode 3 Identifies UPC media catalog number for the disc.
A special mode of Q data is stored within the lead-in area. This Q data contains information on two- or four-channel format, copy
prohibit, and pre-emphasis.
OVERVIEW OF CD TECHNOLOGY | 9