It is now generally accepted that interaction between the laryngeal sound source and pressure Variations m the vocal tract during the glottal cycle can be an important factor in determining voice quality. This interaction can affect both the vibratory pattern of the vocal folds and the glottal air flow pattern for a given vocal fold vibratory pattern. My work has centered around the effect on the glottal air flow for a given vocal fold motion (i.e., the source-tract acoustic interaction), and this will be the focus in this paper as well. I could also mention that the emphasis in this paper will be on an intuitive development of the concepts involved, not on a precise analytic or numerical solution of the differential equations.

A number of studies, including my own, have investigated the ways in which the inertance of the vocal tract air flow tends to modify the waveform of the glottal air flow pulse so as to increase the proportion of energy generated at the closing of the vocal folds. However, the inertance of the vocal tract air flow becomes the clearly dominant factor in source-tract acoustic interaction only when the lowest formant frequency, F₁, is at least about three times the voice fundamental frequency, F_o.

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