Changing pitch and duration in LPC synthesized speech using multipulse excitation

Abstract

Pitch and duration changes are fairly simple to realize in pitch-excited LPC vocoders. Recent work [Atal and Remde, Proc. ICASSP 82, pp. 614–617) has shown that use of multi-pulse excitation provides a significant improvement in the quality of synthetic speech. However, procedures for changing pitch with multi-pulse excitation are not known. We discuss methods for introducing pitch and duration changes in speech synthesized with multi-pulse excitation. Pitch is changed by modifying the length of individual pitch periods. Two methods of adjusting the period length were investigated: one by linear scaling of the time axis of the multi-pulse excitation, the other, by adding or deleting zeros in the excitation. The second method produced very little distortion in the synthetic speech, except in those cases where there was a significant interaction between the first formant and the pitch frequency. The scaling of the time axis produced significantly more distortion. Duration changes are accomplished by adding or removing pitch periods. The LPC area parameters and the amplitude of the major excitmion pulse are interpolated as necessary in creating additional pitch periods.