Red Book is the standard for audio CDs (Compact Disc Digital Audio system, or CD-DA) an audio content medium digitized at 44,100 samples per second (44.1KHz) and in a range of 65,536 possible values or 16 bits. It allowed up to 79.57 minutes of digital audio on one disc or 99 tracks. The format was developed by Sony and Philips in the 1980’s which became the audio medium standard for decades, until the mp3 format was intruded in the late 90’s. The CD replaced tradition audio tape and was the rage for its low noise floor with high digital sound quality.
The term “Red Book” is named after one of the Rainbow Books, a series of books (bound in different colors) that contain the technical specifications for all CD and CD-ROM formats, such as the tracks, sectors, block layout, coding, and sampling.
The Red Book disc is divided into 3 primary sections which are: lead in, program, and lead out. Every CD has a TOC (Table of Contents) which is stored in the Lead In area of CD disc. This records every track on the disc to recall.
Red Book Audio Specifications
The basic specifications state that:
- 1. Maximum playing time is 79.8 minutes
- 2. Minimum duration for a track is 4 seconds (including 2-second pause)
- 3. Maximum number of tracks is 99
- 4. Maximum number of index points (subdivisions of a track) is 99 with no maximum time limit
- 5. International Standard Recording Code (ISRC) should be included
The Red Book specifies the physical parameters and properties of the CD, the optical “stylus” parameters, deviations and error rate, modulation system (eight-to-fourteen modulation, EFM) and error correction (cross-interleaved Reed-Solomon coding, CIRC), and subcode channels and graphics.
It also specifies the form of digital audio encoding: 2-channel signed 16-bit Linear PCM sampled at 44,100 Hz. This sample rate is adapted from that attained when recording digital audio on PAL videotape with a PCM adaptor, an earlier way of storing digital audio.
An audio CD can represent frequencies up to 22.05 kHz, the Nyquist frequency of the 44.1 kHz sample rate.
2 channels 44,100 samples per second per channel — 16 bits per sample = 1,411,200 bit/s = 1,411.2 kbit/s.
On the disc, the data are stored in sectors of 2352 bytes each, read at 75 sectors per second. Onto this the overhead of EFM, CIRC, L2 ECC, and so on, is added, but these are not typically exposed to the application reading the disc.
Some do so for extra features such as DualDisc, which includes both a CD layer and a DVD layer whereby the CD layer is much thinner, 0.9 mm, than required by the Red Book, which stipulates a nominal 1.2 mm, but at least 1.1 mm. Philips and many other companies have warned them that including the Compact Disc Digital Audio logo on such non-conforming discs may constitute trademark infringement. Either in anticipation or in response, recent copy-protected CDs bear stickers and warnings that the CD is not standard and may not play in all CD players, and no longer display the long-familiar logo.