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Spectral Envelope and Phase Optimisation for Sinusoidal Speech Coding

This paper investigates three possible sources of distortion in speech produced by low bit-rate sinusoidal transform coding (STC). These are: (i) the minimum phase assumption. (ii) the spectral envelope derivation and (iii) frequency spreading due to pitch-frequency variation. It is shown that the distortion may be reduced by modifiing the spectral envelope before it is encoded and the use of optimisation to achieve this reduction is discussed . The shape of the reconstructed speech waveform is improved by these techniques and improvement in perceptual qudity is obtained.