A robust vocoder with pitch-adaptive spectral envelope estimation and an integrated maximum-likelihood pitch estimator

This paper describes a low bit-rate vocoder designed for improved speech reproduction quality and robustness. The vocoder includes a new algorithm, the Spectral Envelope Estimator, which forms the nucleus of the spectral analyzer. In addition to estimating the speech spectrum, the spectral analyzer also allows determination of a continuous estimate of the background noise spectrum which may be used for noise suppression. A maximum-likelihood pitch estimator, which shares the signal processing of the spectral envelope estimator, has been integrated into the vocoder to yield accurate pitch estimates of noisy speech. This system yields high quality speech reproduction at bit rates of 2.4 and 8.8 kbps.