On a pitch alteration technique of speech using the asymmetry weighted window

To use the speech as an effective communication medium between man and machine, the synthetic speech must have good quality and various voice colors. Speech synthesis coding is classified into three categories: waveform coding, source coding and hybrid coding. To obtain synthetic speech with high quality, synthesis by waveform coding is desired. However, it is difficult to alter the excitation for various voice colors in waveform coding, because it does not divide the speech into excitation and formant components. Thus it is required to alter the excitation (pitch) in waveform coding for synthesis techniques with high quality and various voice colors. This paper examines the method for both improving and indicating the problem of the PSOLA pitch alteration method. It points out the fact that the spectrum distortion appeared because the Hamming window is not appropriate to the characteristic of the glottal wave shape. Therefore the asymmetric weighted window is proposed in order to improve this defect. The experimental procedure is as follows; first, the speech is segmented by the pitch unit with the asymmetric weighted window, and then the segmented speech is synthesized. The results of an experiment with two male speakers and the two female speakers uttering the test sentences are discussed. According to the experimental results, in the case of using the asymmetric weighted window, synthesized speech of high quality with minimum spectrum distortion can be obtained from waveform coding.