Toward the use of the inverse filter as a diagnostic aid

Abstract

A preliminary investigation using degraded synthetic vowel sounds has shown the digital inverse filter (IF) to have significant ability to relate quantitative information about aberrant laryngeal behavior manifested in the acoustic speech output. The information was contained in the positions of the IF polynomial zeros in the z plane and in the consistency of the root placements as the IF was computed repeatedly over consecutive 25.6 ms analysis segments of the utterance. The analysis resulted in a graphic display of the complex z-plane roots and a vector of pattern features extracted from that display for each of several experimental cases. The pattern of zeros could be used to empirically relate information about underlying perturbation processes. To supplement visual processing, the feature vectors from a large collection of pole plots were used by a clustering procedure to determine the resolution of cases in the feature space. Significant for clinical application is the fact that the technique readily discriminated patterns of simulations of the four acoustic hoarseness types suggested by Yanagihara [N. Yanagihara, J. Speech Hear. Res. 10, 531–541 (1967)].