(
Adaptive
Differential
PCM) A widely used variation of PCM that codes the difference between sample points like differential PCM (DPCM), but can also dynamically switch the coding scale to compensate for variations in amplitude and frequency. See
PCM,
DPCM and
sampling.
ADPCM for CD-ROMs
Sony and Philips set the encoding standards for the CD (Red Book) and CD-ROM (Yellow Book), and several ADPCM codecs were defined for mixing audio and data on a CD-ROM. Because of the larger sampling rates and two channels (left and right stereo), the following bit rates are much larger by comparison to the subsequent list of ADPCM codecs used for speech (the G. standards).
Sampling
Audio Coding Rate Bit Rates
Format Method (kHz) (kBps)
CD-DA (music CD) PCM 44.1 1411.2
CD-ROM Level A ADPCM 37.8 604.8
CD-ROM Level B ADPCM 37.8 302.4
CD-ROM Level C ADPCM 18.9 151.2
ADPCM for Speech Codecs
The ITU has defined numerous speech codecs, some of which use ADPCM. Note the lower bit rates for these applications because of the smaller sampling rates.
Codec Sampling
G. Coding Rate Bit Rates
Number Method (kHz) (kBps)
G.711 Mu-Law PCM 8 64
G.711 A-Law PCM 8 64
G.721 ADPCM 8 32
G.722 ASPCM 7 48/56/64
G.722.1 MLT 16 24/32
G.722.2 ACELP 16 from 6.6
to 23.85
G.723 (withdrawn)
G.723.1 MP-MLQ 8 6.3
G.723.1 ACELP 8 5.3
G.726 ADPCM 8 16/24/32/40/64
G.727 ADPCM 8 16/24/32/40/64
G.728 LD-CELP 8 16
G.729 CS-ACELP 8 8