ADPCM

ADPCM

(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
 Format         Method   (kHz)   Bit Rates (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
 Number   Method    (kHz)   Bit Rates (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    9 bit rates (6.6-23.85)
 G.723    (withdrawn)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

---

ADPCM

(communications)

adaptive differential pulse-code modulation

---

ADPCM - Adaptive Digital Pulse Code Modulation