Some Acoustic Measures of the Fundamental Periodicity of Normal and Pathologic Larynges

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Abstract
Pitch perturbations were computed by measuring the differences between the durations of adjacent fundamental periods from recorded acoustic waveforms. Sound-synchronized highspeed motion pictures of the vocal cords were also taken with a laryngeal mirror. It was found that pitch perturbations reflect variations in the waveshape of the glottal area wave, as well as variations in glottal periodicity. Perturbations having an absolute value > 0.5 msec are apparently induced by transients in the air-pressure drop across the glottis, which may in turn be caused by changes in vocal-tract configurations. Speakers with longer fundamental periods tend to have larger perturbations. The pitch perturbations of 23 speakers with pathologic larynges were measured. Certain of the speakers who had pathologic growths on their vocal cords had larger pitch perturbations than did normal speakers with the same median fundamental periods. The "perturbation factor," which was defined as the percent that perturbations > 0.5 msec occurred, was computed for each speaker. The magnitude of the perturbation factor may serve to detect certain types of pathologic laryngeal conditions.

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