Use of an interactive laboratory computer to study an acoustic-oscillator model of the vocal cords

A Honeywell DDP-516 computer is used with an interactive program to study an acoustic-oscillator model of the vocal cords. The program includes a simulated vocal tract. Iterative solutions are obtained to difference equations which describe the acoustic volume velocity through the cords and the sound pressure output at the mouth. The results can be printed, displayed on a scope, or D/A converted for auditory assessment. A fast Fourier transform provides spectral analysis of the synthesized signals. Parameters that the experimenter can specify from the console include, 1) subglottal pressure, 2) vocal cord tension, 3) vocal tract shape, 4) air density and 5) sound velocity. Results show that tract configuration, and hence acoustic load on the cords, substantially influences fundamental frequency of voicing. Fundamental frequency is also found to be a monotonic function of sub-glottal pressure and cord tension, other factors being constant. Increasing air density tends to reduce fundamental frequency, while changes in sound velocity affect it negligibly.