Speech coder using phase equalization and vector quantization

Abstract

A new speech processing and coding method is proposed which makes use of perceptual redundancy for slowly varying short-time phase characteristics. The method employs waveform conversion through a phase-equalizing filter, which is based on the time domain matched filter for the residue of Linear Predictive Coding (LPC). Phase-equalized speech is found to be almost perceptually equivalent and to be efficiently encoded by a two-stage quantization. In the first stage, vector quantization is performed for the pulse pattern in the time domain. In the second stage, vector-scalar quantization is applied to the spectral components using adaptive bit allocation. The proposed coder is proven to be superior to other coders both in terms of the SNR and the subjective quality. The averaged subjective quality at 9.6 kbps is comparable to that of a 6 bit log PCM.