Vowel normalisation : an interface between acoustic and linguistic descriptions of speaker characteristics in Australian English

Abstract

This thesis examines existing normalisation procedures against the background of a theoretical model of inter-speaker formant variability, which describes observed formant differences in three major categories: phonetic variation, non-uniform variation, and uniform variation. A new normalisation strategy based on this model is proposed which involves the removal of uniform and non-uniform components of inter-speaker variation in order to isolate phonetic variation. The nature of this nonuniformity is subject to empirical investigation. Working along the above strategy, the method adopted in this thesis is to initially acquire a phonetically stable vowel database, which is then screened for phonetic variations through a rigorous phonetic control procedure. The resulting data, now considered to be phonetically homogeneous, are used for exploring two essential domains of inter-speaker variability that contribute to the designing of a future normalisation procedure: (1) By applying uniform transformations using a variety of published scaling parameters, the most effective uniform scaling parameters are identified. (2) Non-uniform inter-speaker variation patterns are analysed and compared with the published results of Fant (1975). A major discovery is that non-uniform inter-speaker variation patterns obtained from phonetically controlled data are grossly different from those observed by Fant. The present database comprises 594 vowels in the /h_d/ word context (11 phonemic monophthongs x 9 speakers x 6 repetitions), and the speakers include 4 adult females, 3 adult males and 2 children (male).