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G.722 Wideband Audio Coder Software for Texas TMS320C54x/C55x DSPs

The ITU G.722 audio coder is intended for wideband (50Hz - 7000Hz) audio signals. The sample rate is 16kHz with 15-bit samples, and the compression is to 64kb/s. Of this 8 or 16kb/s can be masked out in transmission to send auxiliary data information, at a small loss in audio quality after decoding. The algorithm is capable of sending multiple voice signals and sounds clear with loudspeakers. Music also codes with good quality given the bandwidth restriction. Applications include video conferencing and high quality telephony. The algorithm uses Adaptive Differential Pulse Code Modulation (ADPCM) in a backwards configuration. Delay is low, the encoder output being a code adaptively quantised from the current input sample and the coder memory.

The Algotron implementation has been developed to have very low DSP resource usage whilst still passing the G.722 test vectors. The encoder and decoder routines are operated as separate items with individual main subroutine calls. Both should be called every 8kHz. The encoder requires 2 successive input samples, and generates a single 8-bit ADPCM code per call, ie so the data rate is 64kb/s regardless of mode. The decoder input is an 8-, 7-, or 6-bit code depending on the bit rate mode of 64, 56, or 48kb/s. A further subroutine call can be made for initialisation of encoder or decoder. The code routine calls are re-entrant to allow multi-channel operation, the memory block associated with each channel being pointer-addressed. A comprehensive user's guide is provided with the code.

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Availability: NOW, with implementer's guide - integration support offered