From sound to articulation
Bishnu Saroop Atal · The Journal of the Acoustical Society of America · 1977
Methods for determining the shape of the vocal tract directly from acoustic information in the speech signal are of considerable importance in speech research. This paper will review the nature of the articulatory-to-acoustic transformation in the vocal tract and will discuss the present status of research on methods for inverting this transformation. The discussion will include techniques such as analysis-by-synthesis, nonlinear regression, computer-sorting and table look-up procedures. The problem of ambiguous mappings, in which different vocal tract shapes have identical acoustics, will also be discussed. Mathematical procedures for systematically studying the ambiguities will be presented. It will be shown that the acoustic-to-articulatory relationship is multivalued for many cases of interest. For example, the frequencies and amplitudes of the first three formants do not determine the vocal tract shape uniquely; a knowledge of additional articulatory constraints on the vocal tract shape is needed to resolve the ambiguities.