A Numerical Analysis of Glottal Sound Source based on Distributed Parameter Model of Vocal Fold

An 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 fold is represented by an elastic body, which has an effective mass of the vocal fold and is supported by distributed elements composed of a nonlinear spring and damper. The speech production process is simulated by numerically solving equations of nonlinear compressible viscous fluid coupled with motion of vocal fold excluding effects of the collision of each vocal fold to simplify an analysis. 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. Summary, a proposed model is useful for a description of glottal source dynamics, although there remain a problem of taking account of effects of the collision between the both vocal folds.