Vocal tract simulations based on fluid dynamic analysis

Abstract

An alternate approach to speech synthesis based on direct numerical solution of Navier–Stokes (NS) and Reynolds‐averaged‐Navier–Stokes (RANS) equations is described. Unlike the traditional methods based on linear acoustic theory, the NS and RANS formulations are not limited by the assumptions of linearity, negligible viscous effects, and plane‐wave propagation. The expected results are high‐quality synthesis and a new parametrization of speech for applications in automatic recognition and low bit‐rate coding resulting from a parsimonious modeling of articulatory shapes and dynamics. In the present formulation, the Navier–Stokes equations are discretized and solved using a finite‐difference method. An initial application involves a 2‐D simulation of flow through ideal channels (straight, dilating, and constricting tubes) with rigid walls and constant boundary conditions (constant flow velocity at inlet, zero pressure at outlet). As expected for these simple geometries, the resonance frequencies correspond to those predicted by linear acoustics. In a second application, the formulation is applied to the geometry of the three cardinal vowels. For these cases, periodic inflow boundary conditions are also used (a train of short pulses to represent vocal cord excitation). Synthetic speech sounds of encouraging quality are obtained for the three vowels. [Research supported by NSF/ARPA IRI‐9314946 and ARPA DAST 63‐93‐C‐0064.]