Akira Sogo

Voice synthesis system utilizing a transfer function

A voice synthesis system is fundamentally configured by a sound-source model, which simulates human voices and the like, and a voice-path model which simulates properties of voice paths between vocal cords and lips. The sound-source model is embodied by a code book which stores a plurality of code words, representative of waveform patterns, with respect to each of the voices. Each of the code words is selected by an information index. The voice-path model is embodied by a full-pole synthesis filter whose characteristic curve provides multiple poles, each of which is represented by polar coordinates. There is further provided a pitch filter and an all-pass filter. Data representative of the code word selected is supplied to the pitch filter, in which a first delay time, set by a number of delay-time units, is imparted to the data. Then, the all-pass filter imparts a second delay time, which is smaller than the delay-time unit, to the data in response to pitch-variation information. Those filters are provided to perform a fine adjustment of the pitch of the data. Thereafter, the full-pole synthesis filter performs filtering processing on the data in accordance with a coefficient which is set in response to the polar coordinates and pitch-variation information. Thus, signals indicative of synthesized sounds are produced by the full-pole synthesis filter.