Source-System Interaction in the Vocal Tract
James L. Flanagan, D. I. S. Meinhart · The Journal of the Acoustical Society of America · 1964
Acoustic analyses of the vocal system conventionally assume separability of the voiced-sound source and the system. That is, the tract configuration and its driving-point impedance are assumed to influence the acoustic volume flow at the glottis negligibly. Some interaction between the glottal source and the tract is known to occur, however. Toward estimating this interaction and its potential importance to speech naturalness, a computer simulation is made of glottal-source operation. The nonlinear (flow-dependent) properties of the glottal impedance are used to calculate the acoustic volume velocities at the glottis and mouth for a simple vocal configuration. Glottal-area functions, obtained from high-speed photography, are supplied as parameters to nonlinear difference equations with non-constant coefficients. From known initial conditions, the equations are iterated to reach steady-state solutions. The calculated glottal velocities are compared for negligible vocal-tract input impedance and for a low-frequency approximation to a realistic load. The influence of physiological parameters such as subglottal pressure and vocal-cord thickness are also considered.