Vowel normalization by linear transformation of each speaker's acoustic space
Richard A. Harshman, George J. Papcun · The Journal of the Acoustical Society of America · 1976
Different speakers uttering phonetically equivalent vowels will not, in general, produce the same set of formant frequencies. Some of these variations are due to global differences in the shape of the acoustic space from one speaker to the next. We have investigated a family of linear transformation techniques for removing these global variations while preserving intervowel relationships. Patterns of interspeaker variation are first determined by PARAFAC three-way factor analysis of the formant × vowel × speaker data set. The resulting factors suggest dimensions of consistent interspeaker variation which may eventually be identified with physiological or psychological factors affecting vowel production. For the purpose of normalization, each speaker's space is stretched in the directions of the (usually oblique) factor axes, in amounts inversely related to the person-weights on the factors. This produces a restricted “least squares” optimal removal of individual differences due to these linear common factors of speaker variation. The effects of this normalization procedure will be demonstrated with data from several languages and compared with the results of Gerstman's range equalizing technique and Wakita's tract length normalizing technique. [Work supported by NSF.]