Perceived pitch of synthesized voice with alternate cycles

Both in normal speech voice and in some types of pathological voice, adjacent vocal cycles may alternate in amplitude or period, or both. When this occurs, the determination of voice fundamental frequency (defined as number of vocal cycles per second) becomes difficult. The present study attempts to address this issue by investigating how human listeners perceive the pitch of alternate cycles. As stimuli, vowels /a/ and /i/ were synthesized with fundamental frequencies at 140 Hz and 220 Hz, and the effect of alternate cycles was simulated with both amplitude- and frequency-modulation of the glottal volume velocity waveform. Subjects were asked to judge the pitch of the modulated vowels in reference to vowels without modulation. The results showed that (a) perceived pitch became lower as the amount of modulation increased, and the effect seems to be more dramatic than would be predicted by existing hypotheses, (b) perceived pitch differed across vowels, fundamental frequencies, and modulation types, that is, amplitude versus frequency modulation, and (c) the prediction of perceived pitch was best made in the frequency domain in terms of subharmonic-to-harmonic ratio. These findings provide useful information on how we should assess the pitch of alternate cycles. They may also be helpful in developing more robust pitch determination algorithms.