A multi-rate transcoder

The authors describe a single-chip, half-duplex multirate transcoder device. The device is pin selectable as a 32-kb/s ADPCM (adaptive differential pulse code modulation) transcoder and a 16-kb/s subband coding transcoder, and it provides a 64-kb/s PCM passthrough option. The transcoder implementation is fully compatible with the 32-kb/s ADPCM standard defined by ANSI and CCITT recommendation G.721 bis. The subband coder (SBC) algorithm provides a high-quality, cost-effective medium bit-rate solution. The ADPCM and SBC implementations on the device produce toll quality speech.<
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