CD-DA

CD-DA (Compact Disc Digital Audio, 数字音频光盘) is an application format for pre-recorded audio CDs, jointly developed by Philips and Sony; its foundational specifications are commonly referred to as the “Red Book.” It entered the market in 1982 alongside commercial CDs and was later incorporated into standards such as IEC 60908. The term “music CD” commonly refers to CD-DA, while “CD” itself encompasses media and specifications with different purposes, such as CD-ROM, CD-R, and CD-RW.

CD-DA records stereo linear pulse-code-modulated (PCM) audio at a sampling rate of 44.1 kHz and a quantization depth of 16 bits, with a raw data rate of 1,411.2 kbit/s. The specification does not use perceptual coding such as MP3 or AAC; nor is the PCM data on the disc pre-packaged into WAV files. When a computer rips a track, it reads the audio sectors and then writes the continuous sample data to WAV, AIFF, FLAC, or other file formats. The audio data is arranged along a continuous spiral track on the disc. CD-DA reads 75 sectors per second; each audio sector contains 2,352 bytes of main data, corresponding to 1/75 of a second of stereo PCM. Tracks are not independent files but are identified by their starting positions in the directory table; There may be silence between tracks, or they may transition seamlessly. Index points can also mark positions within a single track, though most commercial recordings use only the basic index required for the track start.

In addition to the main audio data, CD-DA includes eight subcode channels labeled P through W. Channels P and Q carry information such as track boundaries, timestamps, directory entries, and control flags, while the other channels are available for graphical or text-based extensions. CD-Text writes characters such as album titles, artist names, and track titles into the subcode area, but this is a later extension and is not supported by every CD or player. Control information such as pre-emphasis flags, copying permissions, and data track flags is also carried by the corresponding subcode channels.

Disc reading uses interleaved Reed-Solomon codes for error detection and correction, and interleaving disperses consecutive physical defects across different time positions. Minor scratches or localized read failures may be corrected; when errors exceed the redundancy capacity, audio devices may employ processing such as interpolation, holding the previous value, or muting. The error-correction goal of CD-DA is to maintain continuous playback, which differs from the CD-ROM data track, which requires byte-by-byte restoration of consistent content.

Standard 120-millimeter audio CDs originally had a typical capacity of approximately 74 minutes of playback time; later, widely used discs could reach approximately 80 minutes. The specific available playback time depends on track spacing, recording range, and mastering parameters. CD-DA can also exist on hybrid discs or Enhanced CDs, but the arrangement of data and audio tracks, session structure, and content visible on traditional players are defined separately by the corresponding extension specifications.