Although the multipulse model is conceptually simple, the problem of locating the pulses is computationally complex. The authors discuss the basic multipulse model and describe a procedure to compute the excitation with optimally adjusted amplitudes. The algorithm provides a framework for computing multipulse excitation with varying degrees of optimization and computational complexity. The authors find that speech quality depends on the pulse rate. They also find that for the same quality, female speech requires a higher pulse rate than male speech. The pitch dependence can be reduced and speech quality improved for high-pitched speakers by incorporating long delay prediction in the multipulse model. >

Amplitude optimization and pitch prediction in multipulse coders

Both multipulse and stochastic coders render telephonic, or close to telephonic quality, for speech signals. Stochastic coders are more efficient from the point of view of bit rate and multipulse coders are the most efficient ones if we are looking for low computational cost. In this paper we study some possibilities of coding speech using the multipulse model but as efficiently as the stochastic coders does. Synthetic speech is generated from a multipulse sequence, obtained from a codebook, through a LPC syntesis filter. Then the model for speech signal is the multipulse model; it resembles the stochastic one in that the input sequence is obtained from a codebook but differs since it does not use pitch filter.

Vector quantized multipulse-LPC

A conceptually new approach for describing the excitation signal in multipulse-excited LPC has been developed. The information needed to determine the excitation for each frame is transmitted to the receiver in the form of a crosscorrelation function. With the help of the LPC filter parameters, the receiver computes the excitation pulse sequence needed to generate the reconstructed speech waveform. Both the crosscorrelation function and the set of LPC parameters are coded by vector quantization. We utilize a classified codebook assignment technique in VQ for the crosscorrelation. This paper describes the coder structure, the use of vector quantization, and the results of computer simulation studies.

H. Koyama

Papers

Fully vector-quantized multipulse LPC at 4800 bps