Interaction mechanisms between glottal source and vocal tract in pitch glides

A computational model for vowel production has been used to simulate rising pitch glides in the time domain. Such glides reveal multi-faceted nonlinear system behaviour when the fundamental frequency fo is near the first vocal tract resonance fR1. There are multiple physical mechanisms for how the acoustic field in the vocal tract can interact with vocal fold dynamics causing this behaviour. The model used in this work includes the direct impact of the acoustic pressure on the transversal plane of the vocal folds and an acoustic perturbation component to the glottal flow. Simulations indicate that both of these mechanisms, when applied separately, cause similar perturbations in phonation parameters when fo crosses fR1. Enabling both mechanisms simultaneously tends to make the separately emerging features more prominent. In simulated glottal flow waveforms, the tendency towards a formant ripple increases when acoustic feedback to glottal flow is enabled, whereas the phenomenon occurs more rarely as a result of the direct acoustic pressure to vocal folds. In all cases, the formant ripple is more pronounced for frequencies below fR1.