Computer Model to Characterize the Air Volume Displaced by the Vibrating Vocal Cords

We use a vocal-cord/vocal-tract model devised earlier to study acoustic effects of the air volume displaced by the vibrating vocal cords. We consider both lateral and longitudinal motion of the cords. We make computer simulations to establish quantitatively the contribution of the displacement current to the total glottal volume velocity (and hence to the total sound excitation for voiced sounds). The displacement current from both lateral and longitudinal motion is found to be second-order by comparison to the total glottal flow. The displacement contribution can, however, be identified in the time waveforms and spectra of the glottal and mouth volume velocities. We use the computer formulation to synthesize speech sounds with and without the displacement current. Auditory observations and spectral calculations on the synthetic output show the displacement current to be discriminable only in close differential comparisons.