THE IMPLEMENTATION OF G.726 ADPCM ON TMS320C54X DSP

Adaptive Differential Pulse Code Modulation (ADPCM) is an efficient way to

digitally code waveforms for telecommunications speech compression

applications. However, unlike voice encoders (vocoders) that use properties of

the human voice in order to reconstruct the waveform, ADPCM is not limited to

the compression of the human voice and can be applied to all waveforms,

high-quality audio, image, and modem data.

This application note describes how to implement the G.726 ADPCM standard

(which includes the G.721 and G.723 recommendations) proposed by the

International Telegraph and Telephone Consultative Committee (CCITT) with the

TMS320C54x, a low-power, enhanced architecture Digital Signal Processor (DSP).

Through implementation of this standard, 8-bit PCM words are reduced to 4-bit

ADPCM words reducing the bit flow by a factor of two. Rate switching during

execution and the implementation of several channels simultaneously in

real-time processing enabled through the dynamic allocation of memory are also

discussed.

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