Nonlinear source-filter coupling in phonation: vocal exercises.
Nonlinear source-filter coupling has been demonstrated in computer simulations, in excised larynx experiments, and in physical models, but not in a consistent and unequivocal way in natural human phonations. Eighteen subjects (nine adult males and nine adult females) performed three vocal exercises that represented a combination of various fundamental frequency and formant glides. The goal of this study was to pinpoint the proportion of source instabilities that are due to nonlinear source-tract coupling. It was hypothesized that vocal fold vibration is maximally destabilized when F(0) crosses F(1), where the acoustic load changes dramatically. A companion paper provides the theoretical underpinnings. Expected manifestations of a source-filter interaction were sudden frequency jumps, subharmonic generation, or chaotic vocal fold vibrations that coincide with F(0)-F(1) crossovers. Results indicated that the bifurcations occur more often in phonations with F(0)-F(1) crossovers, suggesting that nonlinear source-filter coupling is partly responsible for source instabilities. Furthermore it was observed that male subjects show more bifurcations in phonations with F(0)-F(1) crossovers, presumably because in normal speech they are less likely to encounter these crossovers as much as females and hence have less practice in suppressing unwanted instabilities.
Titze
Ingo
I
National Center for Voice and Speech, The Denver Center for the Performing Arts, Denver, Colorado, USA. ingo-titze@uiowa.edu
Riede
Tobias
T
Popolo
Peter
P
D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010699:Phonation / Q000502:physiology*; D014732:Vibration; D014827:Vocal Cords / Q000502:physiology*