Sub-band coding with adaptive prediction for 56 kb/s audio.

This paper reports on a continuation of previous work on the digital coding of 7 kHz wideband audio at 56 kb/s. Focus in the present paper is on 5-band sub-band coding (SBC-ADPCM), DPCM with backward adaptive prediction (ADPCM) and, most importantly, on the combination of the two techniques, SBC- ADPCM. The main conclusion of this paper is that SBC-ADPCM, with a fourth- order backward adaptive predictor in each sub-band, performs much better than SBC-ADPCM for both speech and music inputs, with segmental signal-to-noise ratio gains in order of 6 to 8dB. While SNR gains were no higher with two eighth-order predictors that were carefully optimized, small perceptual gains were noticeable with certain inputs.