Use of an auditory model to improve quality or lower the bit rate of speech synthesis systems

摘要

Low bit rate speech coding algorithms are mostly based on the use of voice production models in which vocal tract filters are excited by vectors chosen from fixed and adaptive codebooks. It has been recognized that to improve the perceptual quality of such coders it is necessary to also allow for the pyschoacoustic properties of the human ear. The weighting filter (5, of Fig. 1B) traditionally used for this purpose is sub-optimal as it doesnot explicitly evaluate auditory characteristics. Disclosed in the preferred embodiment of the present invention, the weighting filter is replaced with an auditory model which enables the search for the optimum stochastic code vector in the psychoacoustic domain. An algorithm, which has been termed PERCELP (for Perceptually Enhanced Random Codebook Excited Linear Prediction), is disclosed which produces speech that is of considerably better quality than obtained with a weighting filter. The computational overhead is low enough to warrant the use of this approach in new speech coders.