Speaker characteristics that appear in vowel nasalisation and their change over time

This study was designed to evaluate whether or not previously proposed acoustic measures of vowel nasality are applicable for speaker comparison in a forensic context. Three acoustic parameters were selected and analysed for vowels in nasal and oral phonetic environments: the amplitude difference (in dB) between the first formant and the extra peak caused by nasalisation (<I>A1</I>–<I>P1</I>), and the frequencies (in Hz) of the first formant (<I>F1</I>) and extra peak (<I>Fp1</I>). We analysed eighteen monosyllables and six isolated words uttered by fifty male speakers and recorded through a microphone. Recordings were conducted twice for each speaker at a two to five month interval. Between- and within-speaker variations were examined using the <I>F</I>-ratio and by conducting regression analysis between two recording sessions, respectively. Results revealed that <I>Fp1</I> of front vowels yielded large <I>F</I>-ratio values, which means high speaker-discriminating power and that <I>A1</I>–<I>P1</I> of the vowels in oral contexts showed within-speaker stability over time.