Finite element simulation of diphthongs in three-dimensional realistic vocal tracts with flexible walls

Abstract

During the production of diphthongs, acoustic waves propagate along a time-varying three-dimensional (3D) vocal tract of complex geometry. The shape of the vocal tract walls does not only change because of the action of the articulators to produce a given sound, but also experience an elastic back reaction to the inner acoustic pressure. In this work the Finite Element Method (FEM) is used to simulate these phenomena. The mixed wave equation for the acoustic pressure and acoustic particle velocity expressed in an Arbitrary Lagrangian-Eulerian (ALE) frame of reference is solved to account for acoustic wave propagation in moving domains. The flexibility of walls is considered by solving a mass-damper-stiffness auxiliary equation for each boundary node. Dynamic vocal tract geometries are generated from the interpolation of static 3D vocal tract geometries of vowels, obtained from Magnetic Resonance Imaging (MRI). Some diphthong sounds are generated as examples