Numerical glottal sound source model as coupled problem between vocal cord vibration and glottal flow

Understanding of dynamics of the speech production process may lead to a breakthrough in increasing the quality of synthesized voice and contribute to medical science with respect to treating voice disorder. However, little is known about mechanisms of speech dynamics, in particular about complex interactions of glottal flow and vocal fold vibration. In this paper, a two-dimensional viscoelastic body model of the vocal folds coupled with an unsteady glottal flow is proposed, and we demonstrate the speech production process by using that model. The vocal cord was modeled by distributed mass-spring-damper elements. The speech production process is simulated by numerically solving equations of nonlinear compressible viscous fluid coupled with motion of vocal fold. The results indicated that the upper and lower edges of the vocal fold vibrated with a phase difference. Furthermore, a change in pressure in the larynx synchronized with the vocal fold vibration, and both amplitude and fundamental frequency of the speech wave slightly fluctuated with time. Although we assumed the physical property of left and right part of vocal cords to be symmetry, the each vocal cord vibration indicated some difference. From the obtained results, although there are some problems to be discussed, one may say that the proposed model is valid for the glottal sound source.