Adaptive Differential Pulse Code Modulation
Adaptive Differential Pulse Code Modulation ( ADPCM ), also known as Delta Pulse Code Modulation , is a compressive coding for a signal, which, similar to Differential Pulse Code Modulation ( DPCM ), is based on difference values, and in which the quantization levels are also scaled depending on the signal curve adjusted (adapted). ADPCM was developed in 1973 at Bell Laboratories by P. Cummiskey, NS Jayant, and James L. Flanagan .
In the area of audio signals, ADPCM is used within the framework of various ITU-T standards such as G.726 . In these applications, the output data rate can be dynamically adjusted between 16 kbit / s and 64 kbit / s. Another application example is Digital Enhanced Cordless Telecommunications (DECT) as used in cordless telephones .
functionality
ADPCM is a pulse code modulation with a prediction function. When processing the signal, an attempt is made to predict the further course of the signal within the next section. For the quantization of the signal in the next time step, only the difference between the predicted and real signal is used. This difference formation means that fewer bits can be used to describe the signal.
With this method, both the prediction function and the quantization level are "adapted" anew with each work step. This control loop achieves a better prediction of the signal than with DPCM .
ADPCM is also used when emulating computer and arcade games . See also MAME and Irem M-62 .
Implementations
Well-known implementations are the IMA ADPCM or IMADPCM, Microsoft ADPCM or MSADPCM, Microsoft IMA ADPCM and Apple QuickTime IMA ADPCM.
ITU-T recommendations
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G.721 (withdrawn) 32 kbit / s adaptive differential pulse code modulation (ADPCM)
The content of this recommendation is now covered by the ITU-T G.726 recommendation. - G.726 : 40, 32, 24, 16 kbit / s adaptive differential pulse code modulation (ADPCM)
- G.727 : 5-, 4-, 3- and 2-bit / sample embedded adaptive differential pulse code modulation (ADPCM)
- G.722 : Subband ADPCM for the frequency range from 50 Hz to 7000 Hz with a sampling rate of 16 kHz and quantized with 14 bits
literature
- Andreas Kanbach, Andreas Körber: ISDN - the technology. Interfaces, protocols, services, end systems. 3rd, revised and greatly expanded edition. Hüthig, Heidelberg 1999, ISBN 3-7785-2288-4 .
- Roland Enders: The home recording manual. The way to optimal recordings. 3rd, revised edition, revised by Andreas Schulz. Carstensen, Munich 2003, ISBN 3-910098-25-8 .
Individual evidence
- ↑ P. Cummiskey, NS Jayant, JL Flanagan: Adaptive quantization in differential PCM coding of speech. In: The Bell System Technical Journal. Vol. 52, No. 7, September 1973, ISSN 0005-8580 , pp. 1105–1118, online (PDF; 6.28 MB) ( Memento of the original from June 30, 2014 in the Internet Archive ) Info: The archive link became automatic used and not yet tested. Please check the original and archive link according to the instructions and then remove this notice. .
