Enhancing waveform interpolative coding with weighted REW parametric quantization

This paper presents an efficient quantization technique for the rapidly-evolving waveforms in waveform interpolative (WI) coders. The scheme, based on a parametrization of the rapidly-evolving waveform (REW) magnitude, and analysis-by-synthesis (AbS) vector quantization (VQ) of the REW parameters, allows both higher temporal and spectral resolution of the REW. A perceptually weighted distortion measure takes advantage of spectral and temporal masking and leads to improved reconstructed speech quality, most notably in mixed voiced and unvoiced speech segments. The technique is an important component of the enhanced waveform interpolative (EWI) speech coder at 2.8 kbps that achieves a subjective quality slightly better than that of G.723.1 at 6.3 kbps.