A model for the synthesis of natural sounding vowels

A model has been developed which is designed to preserve some of the naturalness that is usually lost in speech synthesis. A parametrized function is used to produce an approximation to the cross-sectional rea through the glottis. A circuit model of the subglottal and glottal system is used with the supraglottal pressure to generate the glottal volume velocity. The tract used to obtain the supraglottal pressure is represented by its input-impedance impulse response, which can be calculated from the area function of the tract. A convolution of the input-impedance impulse response with the volume velocity determines the supraglottal pressure. The two coupled equations for the volume velocity are solved simultaneously. The output of the model is generated by convolving the resulting glottal volume velocity with the transfer-function impulse response of the tract. This technique preserves the interaction between the glottal flow and the vocal tract, which is usually lost. Comparisons are made between "complete tract loading" and "inductive tract loading." Magnitude spectra of the various pressures and the glottal volume velocity are examined in detail. Effects of varying the glottal parameters are examined for one vowel. Listening tests showed that vowels synthesized with the interaction were preferred as more natural sounding than those without the interactions.