Vowel systems and accent similarity in the British Isles: Exploiting multidimensional acoustic distances in phonetics

We illustrate how a high-dimension feature space typically used in speech technology can be adapted to the phonetic description of vowels in 13 accents of the British Isles. In a previous work (Ferragne & Pellegrino, 2010), we carried out a formant investigation of the vowel systems of the British Isles; due to erroneous formant estimation, two-thirds of the speakers had to be left out. The present article is therefore an attempt to overcome the methodological difficulties brought about by the use of formants. This novel methodology makes use of distances between vowels in the Mel-Frequency Cepstral Coefficient (MFCC) space. First, hierarchical clustering and multidimensional scaling (MDS) are applied, and tree diagrams and MDS plots are displayed in order to make the data phonetically interpretable. By making distances explicit, this approach to acoustic vowel description facilitates the spotting of phonemic mergers and splits. This part of the study is complemented with an exploratory analysis of the duration of some vowel pairs whose members are acoustically very close to each other. Second, correlations between individual vowel distance matrices are computed, yielding an estimate of the acoustic distance between accents. The explanatory power of these distances is then assessed with hierarchical clustering and MDS. Our ultimate goal is to draw a parallel between the findings obtained with our unconventional method and previous phonetic descriptions, and to benchmark this new methodology against the results in Ferragne and Pellegrino (2010).