Adaptive Differential Pulse Code Modulation
Adaptive Differential Pulse Code Modulation (ADPCM ), also called delta pulse code modulation, a compressive coding for a signal which is similar to differential pulse code modulation (DPCM ), based on the difference values, and in addition adapted to the scale of the quantization steps depending on the waveform (adapted ) be. ADPCM was developed in 1973 at Bell Laboratories by P. Cummiskey, NS Jayant and James L. Flanagan.
In the field of audio signals ADPCM place in various ITU-T standards such as G.726 application. The output data rate can be dynamically adjusted between 16 kbit / s and 64 kbit / in these applications. Another example is Digital Enhanced Cordless Telecommunications (DECT) as it is used in cordless phones.
ADPCM is a pulse code modulation with prediction function. In the processing of the signal is trying to predict the further waveform within the next section. So only the difference between the predicted and the real signal is used for the quantization of the signal in the next time step. By this difference the less bits can be used to describe the signal.
In this method, both the prediction function and the quantization at each step is new 'adapted'. Through this loop a better prediction of the signal is achieved than with DPCM.
Even with the emulation of computer and arcade games ADPCM is used. See also M.A.M.E. and Irem M- 62.
Known implementations are the IMA ADPCM or IMADPCM, Microsoft ADPCM or MSADPCM, Microsoft IMA ADPCM and Apple QuickTime IMA ADPCM.
ITU- T recommendations
- G.721 (withdrawn) 32 kbit / s Adaptive Differential Pulse Code Modulation (ADPCM ) The content of this Recommendation is now covered by ITU-T Recommendation G.726.
- 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 )