Estimation of vocal tract input impedance at the glottis from formant measurements

Abstract

It is well known that the mapping from articulation to acoustics is many-to-one or many-to-many, so that so-called “articulatory-acoustic inversion” is a challenging problem. What has not been noted, however, is that the input impedance from the glottis can be determined from the inverted articulatory configuration regardless of whether this configuration is accurate. This can be useful as a step toward estimating the acoustic load on vocal fold vibration during phonation. The theory and procedure for thus obtaining estimates of the vocal tract input impedance is presented, its relation to the Mermelstein/Schroeder method is shown, and its limitations are discussed. Finally, experiments with synthetic and naturally produced vowels are presented and discussed. It is shown that the estimated input impedance is accurate up to the highest measured formant, with the largest deviations centering around the formant frequencies due to errors in formant measurements and the handling of acoustic losses.