ADPCM


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ADPCM

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

ADPCM

This article is provided by FOLDOC - Free Online Dictionary of Computing (foldoc.org)

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).
                        SamplingAudio          Coding   Rate    Bit RatesFormat         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            SamplingG.       Coding   Rate   Bit RatesNumber   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 G.723    (withdrawn)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
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References in periodicals archive ?
The interest of many research workers has been directed towards the ADPCM codec capable of providing better performance for speech and voiceband data signals at high speed, either by modifying the ADPCM algorithm (Benvenuto & Daumer, 1988; Shampiro, 1989; CCITT Recommendation G.726-1990; CCITT Recommendation G.727-1990; ITU-T Recommendation G.726 Appendix III-1994; AL-Rawi & AL-Rawi, 2014), or by modifying the model of data transmission system (Jimaa, 1990; AL-Rawi, Soegijoko, & Samadikun 1997; AL-Rawi, 1998; AL-Rawi & AL-Rawi, 2011).
The resulting output of the QAM transmitter is QAM signal with carrier frequency of 1800 Hz and symbol rate of 2400 baud giving an information rate of 2400 x 4bits = 9600 b/s = 9.6 kb/s to be sent over 32 kb/s ADPCM link in cascade with telephone channel.
A series of computer simulation tests using C programming language have been carried out on the system in Figure 1 with three types of detectors, DR1, DR2 and DR3, to determine their relative tolerance to AWGN when operating over ADPCM link in cascade with telephone channel.
ADPCM decoder uses the additional information for the adaptation of the predictor coefficient.
For the ADPCM system, these two parameters are defined as
Initially, the ADPCM audio decoding chip set will be made available by drive manufacturers and other third parties, such as Optical Media International, on a separate card or piggyback card to a CD-ROM drive interface card.
Marathon is implementing ADPCM around the loop, preferring the one-time equipment charge to the continuing cost of another T1.
"ADPCM will free up bandwidth for some of our upcoming needs.
The ADPCM equipment cost was paid back within four or five months with the roughtly $1000 a month T1 savings.
It is fully compatible with the public network at every level, including DDS substrate formatting and ADPCM (Adaptive Differential Pulse Code Modulation) voice compression.
Rather than send 8 bits to describe the step fully, ADPCM sends 4 bits to describe the change from the last sample.
At present, there is no world standard for ADPCM encoding, but one is expected.