| الملخص: |
A mathematical model was developed to investigate possible causes of jitter and shimmer. The model builds from the classic, lumped element, two-mass model of Ishizaka and Flanagan. Bilateral asymmetry was incorporated into the model to facilitate the simulation of physiological and aerodynamic imbalances in the larynx. The aerodynamic driving forces on the vocal folds were derived from empirical pressure data that were obtained from a scaled-up Plexiglas model of a typical male human larynx, called M5. The mathematical model is based on ten, second-order, nonlinear, coupled, ordinary differential equations that were solved simultaneously using the software Mathematica. The solutions were analyzed graphically and numerically to identify perturbations in the fundamental frequency and amplitude of the glottal airflow. Jitter and shimmer were quantified using the jitter factor and the amplitude variability index. The results indicate that only time-dependent asymmetries result in jitter and shimmer. |
