The impact of breathiness on the intelligibility of speech
The aim of this study is to determine how deterioration of voice quality, such as breathiness, may impact on the intelligibility of speech. Acoustic analysis was conducted on sustained vowel phonation as well as discrete segments taken from recorded sentences, retrieved from a database of voice disordered speakers. Measures included: frequency of the first two formants (F1, F2), singing power ratio, the amplitude difference between the first two harmonics (H1-H2 amplitude difference), voice onset time, and energy ratio between consonant and vowel (CV ratio). A series of two-way (glottal closure x vowel) repeated measures Analysis of Variances conducted on these acoustic measures showed a significant glottal closure (complete vs. incomplete) or glottal closure by vowel interaction effect for the F2 frequency, H1-H2 amplitude difference, and singing power ratio. Based on findings in literature that reported a dominant first harmonic as a useful predictor of breathiness, the measure of H1-H2 amplitude difference was selected as a factor for investigation of the impact of voice quality on the perception of vowel intelligibility and clarity. Fixed-length vowel segments at five levels of H1-H2 amplitude difference were presented to 10 male and 10 female inexperienced listeners between the ages of 19 and 34 years. It was expected that the tokens with a dominant first harmonic, indicative of a more breathy voice, would be associated with a lower rate of correct vowel identification and a lower rate of being perceived as “clearer”. The finding of a change of the perceptual ratings as a function of the H1-H2 amplitude difference will demonstrate the effect of voice quality on vowel intelligibility.