Is the Relationship between Acoustic and Articulatory Variables in Speech Intrinsically Linear?

Abstract

The functional relationship between the acoustic parameters of speech and the positions of different articulators was investigated on a computer-simulated model of the vocal tract using nonlinear regression. The area function of the vocal tract in the model was specified by seven articulatory variables, namely, the area and location of the maximum constriction formed by the tongue body, the area and location of the tongue tip constriction, the area of the mouth opening, lip protrusion, and the length of the vocal tract. It was found that any one of the seven articulatory variables could be represented reasonably accurately by a polynomial function of the acoustic parameters of the vocal tract model. Two interesting properties of this relationship were observed. First, in estimating an artic-ulatory variable, knowledge of the other articulatory variables was not required; the articulatory variable was uniquely determined by the acoustic parameters alone. Second, any one of several different acoustic representations—such as predictor coefficients, formant frequencies, and their band widths, or power spectrum—could be used with equal success in determining articulatory variables. The applications of this method for determining positions of the articulators during speech production, for speech recognition, and for control of articulatory models for speech synthesis are discussed.