Source-filter interaction in phonation: A study using vocal-tract data of a soprano singer

We simulated acoustic interaction between the voice source system in the larynx and the acoustic filter of the vocal tract. The vocal tract of a soprano was first scanned in three dimensions using magnetic resonance imaging while she produced four musical notes (A3, E4, D5, and A5) with /a/ and /i/. These images were used to simulate voice production, including the vibratory motion of the vocal folds and the behavior of glottal airflow. Images for the /i/ vowel were used in the simulation, because a good proximity relationship was found between the fundamental frequency and the first impedance peak of the vocal tract. The simulation results revealed that the fundamental frequency (vibration frequency of the vocal folds) was decreased to a large extent by the interaction especially when their natural frequency was in the proximity of the impedance peak. In a specific case, the acoustic load of the vocal tract exerted on the vocal folds changed as a result of the interaction, so the vibratory motion was effectively assisted. These interaction effects were also examined in terms of the phase relation among the temporal waveforms of the glottal variables.