Determination of vocal tract shape during phonation from input/output measurements of throat-wall vibration near the glottis and microphone pressure at the lips
N. Rao Vemula, A. Maynard Engebretson, D. L. Elliott · The Journal of the Acoustical Society of America · 1980
A reflectionless terminator tube at the lips was used to measure the inside surface response of the throat wall when the wall was mechanically excited with a vibrator. The “acoustic” transfer function characteristic of the wall (relating the supraglottal sound pressure and the “acoustic” component of the wall vibration) revealed by these measurements can be well approximated when the wall, consisting of cartilages, muscles, and soft tissue, is modeled as a lumped-parameter mechanical system. Earlier attempts to obtain the vocal tract shape during phonation have used the speech signal alone and made some simple assumptions about the glottal source. In the present study simultaneous measurements of the inside surface pressure with the terminator tube and of throat-wall external vibration during phonation are made to determine (total) transfer function characteristic of the wall. A pole-zero model for this (total) transfer function characteristic is then used to specify the source signal for a model of the vocal tract. More consistent tract shapes are found using the input/output approach compared to those derived from linear predictor procedures based on the speech signal alone.