Vector/matrix quantization for narrow-bandwidth digital speech compression

Speech compression techniques for very low data rate compression are studied. The techniques are based on a standard LPC analysis/synthesis (vocoder) system. Significant advances are made in the quantization algorithms to achieve bit rates of 200 to 400 bps. Frame predictive vector quantization is developed to compress the bit rate for the LPC model filter top under 250 bps. The vector quantization technique developed applies to continuous speech and is independent of both speaker and vocabulary. An innovative LPC compression technique, matrix quantization, is also developed to compress the LPC model filter to a rate under 150 bps. The design is applicable to continuous speech and unlimited vocabulary. At this stage of development, it is adapted to a single speaker, but theoretically it can be generalized to a selection of speakers or even the general population. Subjective evaluation of both the vector and matrix LPC quantization approaches using the diagnostic rhyme test (DRT) has been performed and the test scores are analyzed in detail. The results indicate that the proposed techniques are feasible for intelligible speech transmission at bit rates of 400 bps and 200 bps.