Perceptual shape VQ of spectral envelope for efficient representation of LPC residual

The authors present an effective spectral envelope (SE) quantisation scheme for parametric speech coders, based on human hearing properties. The variable-dimension SE uniformly sampled vector in frequency is first converted into a fixed, but small, number of nonlinearly spaced frequency bands on the Bark scale. The minimum Bark spectral distortion (BSD) criterion is applied to enable the hearing-based SE vector quantisation (HSEVQ) scheme to quantise the SE vector, achieving a slightly better perceptual quality than the traditional method. A simplified HSEVQ (SSEVQ) scheme is developed by removing some of insensitive functions from the HSEVQ to reduce the complexity of the computation. Simulations reveal that the SSEVQ method reduces the amount of computation of the traditional SE vector quantisation scheme by a factor of nine, while retaining the quality of the reconstructed speech signal.