A measurement study on voice instabilities during modal-falsetto register transition

When one of the dominant harmonics (the fundamental frequency and its harmonic components) is close to the first formant frequency, the effect of the source-filter interaction can induce voice register transition, in which the vocal-fold vibration becomes unstable and the pitch jumps abruptly. We investigated the relationship between the dominant harmonics, the first formant frequency, and the pitch jump width in the modal-falsetto transition to examine the effect of source-filter interaction. We measured temporal patterns of the fundamental frequency and the first formant when subjects performed rising glissandi with /a/ and /i/ vowels. For the /a/ vowel, there were weak proximity relationships between the dominant harmonics and first formant during the transition, indicating that source-induced transition occurred. For the /i/ vowel, in contrast, the fundamental frequency was regularly close to the first formant in the transition, indicating that the acoustically induced transition was caused by the source-filter interaction. Additionally, it was found that the difference between these two mechanisms had little influence on the pitch jump width. Finally, we concluded that the source-filter interaction is a contributory factor of the modal-falsetto transition, in agreement with foregoing studies.