Intra- and inter-speaker variability of vowel space using three different formant extraction methods

Individual speakers’ voices display various unique patterns, one of the most prominent of which is vowel articulation. This study focuses on vowel space properties of 15 Czech speakers in read and spontaneous speech, comparing outputs of three formant extraction methods, measuring formants: (1) in the vowels’ temporal midpoints, (2) as their mean from the vowels’ middle thirds, and (3) in the vowels’ articulatory targets. The results show extensive variability across speakers, but also great within-speaker variability between the two speech styles, with spontaneous speech manifesting more centralised vowel pronunciation than read utterances. The first two measurement methods did not yield systematically different results, while formant values extracted from acoustically defined articulatory targets lead to noticeably larger vowel spaces. The results suggest that care should be taken when interpreting formant values obtained by different methods.