Voice instabilities in a three-dimensional continuum model of phonation

Abstract

The goal of this study is to identify vocal fold conditions that produce irregular vocal fold vibration and the underlying physical mechanisms. Using a three-dimensional computational model of phonation, parametric simulations are performed with co-variations in vocal fold geometry, stiffness, and vocal tract shape. For each simulation, the cycle-to-cycle variations in the amplitude and period of the glottal area function are calculated, based on which the voice are classified into three types corresponding to regular, quasi-steady or subharmomic, and chaotic phonation. The results show that the presence of a vocal tract significantly increases the occurrence of irregular vocal fold vibration, which naturally occurs even under symmetric vocal fold conditions, in particular for vocal folds with very low transverse stiffness in the coronal plane or a soft vocal fold body layer. The occurrence of voice instability is suppressed by increasing the transverse stiffness, increasing the body-cover ratio in the longitudinal stiffness, or decreasing the subglottal pressure. The implications of these observations on the production of certain voice qualities are discussed. [Work supported by NIH.]