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Voice Digitization

 

Adaptive Differential Pulse Code Modulation (ADPCM)

ADPCM is a very well-defined standard algorithm. The standard is expressed in exact detail and must be implemented exactly to run the test vectors. Some of these tests include inputting digital test bytes, processing them with the algorithm, then checking for proper bit-for-bit output.

The ADPCM algorithm generates a code difference between the current input sample and a predicted value from past output.

The ADPCM process generates 4-bit words, therefore 16 specific bit patterns are generated. The CCITT ADPCM algorithm transmits all 16 possible bit patterns. The ANSI ADPCM algorithm uses 15 of the 16 possible bit patterns (an “all-zeroes” – 0000 pattern is not generated).