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A digital high-speed camera system for the endoscopic examination of the larynx allows recording speeds of up to 5,600 frames/s. Recordings of up to 1 s duration can be stored and used for further evaluation. Combined with an image processing program the system is able to render x-t diagrams of vocal cord movement. Data acquired from different locations of each vocal cord can be plotted separately. All of the known objective parameters of the voice can be derived from highspeed glottograms.

Phonation onset is discussed in the framework of dynamical systems as a Hopf bifurcation, i.e., as a transition from damped to sustained vocal fold oscillations due to changes of parameters defining the underlying laryngeal configuration (e.g., adduction, subglottal pressure, muscular activity). An analytic envelope curve of the oscillation onset is 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. This parameter reflects the laryngeal state prior to phonation and can be used as a quantitative classification criterion in order to assess the phonation onset in clinical diagnosis. The extraction of the phonation onset time from simulated time series using a simplified two-mass model and from digital high-speed videos is described in detail. It shows a good agreement between theory and measurement.

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