PHONATION ONSET - VOCAL FOLD MODELING AND HIGH-SPEED GLOTTOGRAPHY

Phonation onset is discussed in the framework of dynamical systems as a Hopf bifurcation, i.e., as a transition from damped to sustained voc al fold oscillations due to changes of parameters defining the underly ing laryngeal configuration (e.g., adduction, subglottal pressure, mus cular activity). An analytic envelope curve of the oscillation onset i s deduced by analyzing the Hopf bifurcation in mathematical models of the vocal folds. It is governed by a single time constant which can be identified with the physiological parameter phonation onset time. Thi s parameter reflects the laryngeal state prior to phonation and can be used as a quantitative classification criterion in order to assess th e phonation onset in clinical diagnosis. The extraction of the phonati on onset time from simulated time series using a simplified two-mass m odel and from digital high-speed videos is described in detail. It sho ws a good agreement between theory and measurement. (C) 1998 Acoustica l Society of America.