A new inverse-filtering technique for deriving the glottal air flow waveform during voicing

A method is described for deriving the volume velocity waveform at the glottis during voiced speech by inverse-filtering the volume velocity waveform at the mouth. Unlike the previously used technique of inverse-filtering radiated acoustic pressure, this method provides a signal that is accurate down to zero frequency, not susceptible to low-frequency noise, and easily calibrated in amplitude by a constant air flow. The primary limitation is the need for a transducer that will measure volume velocity at the mouth with adequate fidelity. In this work, volume velocity was recorded from a specially designed circumferentially vented wire screen pneumotachograph mask which provided a time resolution of 1/2 msec, without serious speech distortion. Inverse-filtered volume velocity was recorded with two adult male subjects for voicing in the modal register. Typical results are shown which indicate the way in which the glottal waveform varied with changes of fundamental frequency, subglottal pressure, and a dimension of voice quality related to the degree of compression of the vocal folds. Also considered are the effects of glottal-supraglottal acoustic interaction, and the effect on the glottal waveform of air displaced by the movements of the vocal folds.