Optimizing LPC filter parameters for multi-pulse excitation

Present LPC analysis procedures assume that the input to the all-pole filter is white; the filter parameters are obtained by minimizing the mean-squared error between the filter output samples and their values obtained by linear prediction on the basis of past output samples. It is well known that these procedures often do not yield accurate filter parameters for periodic (or quasi-periodic) signals such as voiced speech. To compensate for the periodic nature of speech, an estimate of the excitation of the all-pole filter has to be made. Multi-pulse LPC obtains the best excitation for a specified bit rate by minimizing a weighted mean-squared criterion representing subjectively important differences between original and synthetic speech signals. In this paper we examine the possibility that multi-pulse excitation can approximate the all-pole filter excitation sufficiently closely and obtain the optimum filter parameters for this excitation.