A study on the influence of prosody and excitation source model on synthetic speech

The paper presents a study regarding two methods for improving the naturalness of synthesized speech. We have modeled the excitation source for an LPC vocoder as an impulse train which is passed through a filter to be formed into the excitation signal. The delay between two impulses can be constant, or it can be modulated by the pitch contour extracted from the original utterance. A Glottal Pulse Filter is extracted from the LPC residual so that its frequency response best fits the spectrum of the residual. Four excitation generators were implemented: two unfiltered and two filtered impulse generators. Synthetic speech obtained using the four generators were evaluated and scored by a group of ten people. Festival voices were also evaluated for reference.