Compact Disc Digital Audio: Difference between revisions

Revision as of 15:55, 7 March 2025

Revision as of 14:30, 25 March 2025

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==== Frames and timecode frames ====

{{MainFurther|Track (optical disc)#Sector structure}}

The smallest entity in a CD is a channel-data ''frame'', which consists of 33 bytes and contains six complete 16-bit stereo samples: 24 bytes for the audio (two bytes&nbsp;× two channels&nbsp;× six samples&nbsp;= 24 bytes), eight CIRC error-correction bytes, and one [[subcode]] byte. As described in {{slink||Data encoding}}, after the EFM modulation the number of bits in a frame totals 588.<!--[[User:Kvng/RTH]]-->

The smallest entity in a CD is a channel-data ''frame'', which consists of 33 bytes and contains six complete 16-bit stereo samples: 24 bytes for the audio (two bytes&nbsp;× two channels&nbsp;× six samples&nbsp;= 24 bytes), eight CIRC error-correction bytes, and one [[subcode]] byte. As described in {{slink||Data encoding}}, after the EFM modulation the number of bits in a frame totals 588.

On a ''Red Book'' audio CD, data is addressed using the ''MSF scheme'', with [[timecode]]s expressed in minutes, seconds and another type of ''frames'' (mm:ss:ff), where one frame corresponds to 1/7575th of a second of audio: 588 pairs of left and right samples. This timecode frame is distinct from the 33-byte channel-data frame described above, and is used for time display and positioning the reading laser. When editing and extracting CD audio, this timecode frame is the smallest addressable time interval for an audio CD; thus, track boundaries only occur on these frame boundaries. Each of these structures contains 98 channel-data frames, totaling 98 &nbsp;× 24 &nbsp;= 2,352 bytes of music. The CD is played at a speed of 75 frames (or sectors) per second, thus 44,100 samples orand 176,400 bytes per second.<!--[[User:Kvng/RTH]]-->

In the 1990s, [[CD-ROM]] and related [[ripping|Digital Audio Extraction]] (DAE) technology introduced the term ''[[CD-ROM#CD-ROM format|sector]]'' to refer to each timecode frame, with each sector being identified by a sequential [[integer]] number starting at zero, and with tracks aligned on sector boundaries. An audio CD sector corresponds to 2,352 bytes of decoded data. The ''Red Book'' does not refer to sectors, nor does it distinguish the corresponding sections of the disc's data stream except as "frames" in the MSF addressing scheme.