Scaling of waveform segments along the time axis for concatenative speech synthesis

Waveform scaling along the time axis is introduced as a pitch and duration conversion method for concatenative speech synthesis. This method will affect F_0, duration and spectrum, although no degradation of the naturalness is caused when the scaling ratio is nearly 1. In corpus-based concatenative speech synthesis, when there are many segment candidates with various F₀ values or durations, excessive scaling may be unnecessary. The result of experiments indicated that the difference in F₀ and duration between the target and a selected segment became smaller. However, it also showed that the conventional cost function in selection cannot represent the degradation of naturalness by spectral distortion, and that the scaling range without degradation may not be enough for the pitch conversion required in our synthesizer. These problems should be improved by wider range scaling with a new cost function that also considers the degradation.