UBC Theses and Dissertations
A hybrid model of vocal fold vibration with application to some pathological cases Wong, Darrell
It has been hypothesised (Moore 1976) that vocal fold pathology will manifest itself in voiced sounds when vibratory characteristics are disrupted. This thesis examines the effects that pathologies have on the vocal folds through the use of a computer simulation model of the human phonatory system. A damped, nonlinear, multiple-mass spring model combined with a transmission line vocal tract model, was developed and mathematically simulated on a computer. Configurational parameters were then varied asymmetrically in order to examine the vibratory characteristics of the system. In particular, the glottal flow and speech signals from the glottal and vocal tract subsystems were observed for perturbations. Next, jitter, shimmer, and harmonics to noise ratio analyses were made and the results compared to a database of analysed speech recordings from Vancouver General Hospital. Finally, an approximate mathematical analysis was made examining the underlying nonlinear oscillatory phenomena. The study showed that the model, a hybrid between the simple two mass Ishizaka and Flanagan model (1972) and the more complex Titze (1973, 1974) model, was able to simulate the desired asymmetrical conditions. Perturbation phenomena were successfully simulated and the results found to be in good agreement with both real data and data obtained from previously published models. The mathematical analysis revealed the observed perturbations to be characteristic of second and third order subharmonics found in nonlinear oscillatory systems. It was also shown that the driving forces discussed by Titze (1980) (ie the Bernoulli effect, vertical phasing and vocal tract loading) all appear directly in the proposed dynamical equation.
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