Vector adaptive predictive coding of speech at 9.6 kb/s

We have developed a new speech coder which significantly enhances Adaptive Predictive Coding (APC) by using vector quantization. The coder, called Vector APC (VAPC), gives very good speech quality at 9.6 kb/s and reasonably good quality at 4.8 kb/s. In VAPC, redundancy is first removed by a long-delay predictor and then by a short-delay predictor; the prediction residual is then quantized by a gain-adaptive vector quantizer. In the receiver, decoded residual vectors are used to excite a synthesis filter to obtain the coded speech. The computations required by VAPC are only in the order of 2 to 4 million flops per second. Because of its low complexity and high speech quality, VAPC may offer a low-complexity alternative to Code-Excited Linear Prediction (CELP) at low bit rates.