Acoustic Correlates of Subglottal Activity
Peter Ladefoged · The Journal of the Acoustical Society of America · 1963
The source of power for most speech sounds is the pressure of the air below the vocal cords. This pressure is regulated by the action of the muscles of the respiratory system. A series of electromyographic experiments has shown that bursts of muscular activity, particularly of the internal intercostal muscles, occur during speech. These bursts produce peaks of subglottal pressure that can be correlated with the perceived stress of an utterance. The subglottal pressure variations are perceived also as pitch changes, since they affect the frequency of vibration of the vocal cords. A second set of experiments has shown that an increase in the subglottal pressure causes an immediate increase in frequency, which could not be caused by any adjustment of the laryngeal musculature, since such a reflex action could not have occurred except after a short reaction time. It is shown that the complex variations in fundamental frequency recorded during a phrase are often the product of a varying pressure drop across the glottis and a comparatively simple variation in vocal-cord tension.