Use of fundamental frequencies shaped by generation process model for HMM-based speech synthesis

Generation process model of fundamental frequency (F₀) contours is known to represent global movements of F₀´s keeping a clear relation with linguistic information of utterances. While HMM-based speech synthesis can generate a good quality of speech, problems, which arise from frame-by-frame processing, are pointed out. These problems are expected to be solved by incorporating the model constraints. A method is developed to use F₀ contours approximated by the model for HMM training instead of observed F₀ contours. A clear improvement in the quality of synthetic speech is shown through listening experiments. In the method, fragments of F₀ contours not represented by the model (F₀ residuals) are ignored. A scheme is further introduced to cope with the issue; F₀ residuals are also included in the training and synthesis processes of HMM-based speech synthesis, and the generated F₀ residuals are added to the model-based F₀´s before the waveform generation. The model constraint has another merit; relations between generated F₀ contours and texts are clear, and it is possible to add linguistic information such as emphasis to synthetic speech, or to change speaking styles through manipulating F₀´s in the F₀ model framework. Several experimental results supporting the advantages of the method are shown.