A modified-superposition speech synthesizer and its applications

In speech synthesis, a digital filter is used to generate samples of the acoustic speech waveform. Because of the time-varying nature of speech, filter parameters are updated at frame boundaries. This results in a transient perturbation of synthesized speech whenever parameter values exhibit a large frame-to-frame variation. From the computational point of view, such perturbations are caused by a mismatch which is introduced between the updated filter parameters on the one hand, and the energy contained in the autoregressive part of filtermemory on the other. We propose to use a modified-superposition synthesis strategy, which allows the contribution of this energy as it dies away in the present frame to be computed from the non-updated parameterset. In this way, essentially transient-free speech is obtained. Applications include a robust cascade-type synthesizer for formant vocoding which is immune to formant labeling errors.