Phonetic effects on listener detection of vowel concatenation

Concatenative speech synthesis quality depends in part on the minimization of audible discontinuities between two successive concatenated units. This study focuses on human detection of concatenation discontinuities in synthetic speech. Statistical analyses compared for various phonetic categories the results observed in perceptual tests with two voices – one female and one male. Neither a comprehensive phonetic analysis nor a comparison of discontinuity detection between voices has been reported previously. Although discontinuities were generally more detectable for the female than the male voice, there were many similarities between results obtained from the two speakers. A reliably higher rate of detection of discontinuities was observed for diphthongs than for monophthong vowels. Post-vocalic consonants influenced concatenation discontinuities significantly more than pre-vocalic consonants, and postvocalic sonorants were associated with higher detection rates than post-vocalic non-sonorants. The differences in discontinuity detection among vowels and among consonantal contexts for both voices consistently suggest that highly audible discontinuity is related to concatenation in regions of spectral change.