Perception of synthetic two-formant vowel transitions

Abstract

Speech analysis shows that the second formant transitions in vowel–vowel utterances are not always of the same duration as those of the first formant transitions nor are they always synchronised. Moreover the formant transitions often move initially in a different direction from their final target. In order to investigate whether these deviations from linearity and synchrony are perceptually significant a series of listening tests have been conducted with the vowel pair /a/–/i/. It was found that delays between the first and second formant transitions of up to 30 ms are not perceived, nor are differences in duration of up to 40 ms if the first and second formants start or end simultaneously. If the second formant transition is symmetric in time with respect to the first formant differences of up to 50 ms are tolerated. Excursions in second formant transition shape of up to about 500 Hz are also not perceived. These results suggest that most of the deviations from linearity and synchrony found in natural vowel–vowel utterances are not perceptually significant.