The spectral envelope estimation vocoder

This paper describes a low bit-rate vocoder designed for improved speech reproduction quality and robustness. The vocoder is designed around 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 is 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 is capable of good quality speech reproduction at bit rates down to 2.4 kbits/s.