Computer simulation of pathological vocal-cord vibration

Abstract

A dynamic model of the vocal cords, namely, a bilaterally symmetric two-mass model, is extended to a bilaterally asymmetric two-mass model to simulate pathological conditions of the vocal cords. Asymmetric behavior of the computer model is investigated for various conditions of imbalance in bilateral tension. The computer model is found to behave in three basic vibratory modes that are similar to those observed in physiological experiments on larynges under tension imbalance. The three distinctive modes are (1) a vibratory pattern with differences in phase and amplitude of cord vibration; (2) a nearly periodic motion without glottal closure; and (3) an unsteady, dicrotic or tricrotic motion. The three modes are found to be a strong function of the subglottal pressure and the glottal rest area, as well as the imbalance conditions of the cord parameters. The asymmetric vocal-cord model is incorporated into a dynamic vocal-tract synthesizer to simulate speech with a hoarse voice. Subject Classification: [43]70.20, [43]70.50.