Real time 800 bits/s linear predictive vocoder for HF communications

Describes both simulation and real-time implementation of an 800 bits/s vector quantization LPC vocoder. Vector quantization requires a training algorithm to design efficient codebooks of LP filters (in other words, codebooks that fit the distribution of the input vectors). It also requires a fast nearest neighbour search algorithm for real time encoding of the LP filters. These algorithms are summarized. The hardware configuration is described. It consists mainly of a TMS 32010 processor board and of a memory board. The speech quality and intelligibility at 800 bits/s have been subjectively evaluated with informal listening tests and Diagnostic Rhyme Tests performance results are presented. The performances of this vocoder in the case of HF communications under degraded conditions is briefly evaluated