A new model of LPC excitation for producing natural-sounding speech at low bit-rates

The excitation for LPC speech synthesis usually consists of two separate signals- a delta-function pulse once every pitch penod for voiced speech and white noise for unvoiced speech. This manner of representing excitation requires that speech segments be classified accurately into voiced and unvoiced categories and the pitch period of voiced segments be known. it is now well recognised that such a rigid idealization of the vocal excitation Li often responsible for the unna-tural qualizy a.ssock#ed with synthesized speech. This paper describes a new approach to the excitation problem that does not require a priori knowledge of either the voiced-unvoiced decision or the pitch period. All classes of sounds are generated by exciting the LPC filter with a sequence of pulses; the amplitudes and locations of the pulses are determined using a non-iterative analysis-by-synthesis procedure. This procedure minimizes a perceptual-distance metric representing subjectively-important differences between the waveforms of the origi-nal and the synthetic speech signals. The disiance metric takes account of the finite-frequency resolution as well as the ditTerential sensitivity of the human ear to errors in the formant and inter-formant regions of the speech spectrum