Referential Vowel Duration Ratio as a Feature for Automatic Assessment of L2 Word Prosody

This paper proposes a referential vowel duration ratio for a pair of vowels in consecutive syllables and a weighted mean of the referential vowel duration ratios on a logarithmic scale as a feature for automatic assessment of second-language (L2) word prosody. In addition to contours of fundamental frequency (F0) and energy i.e. suprasegmental information of speech, segmental duration of syllables or phonemes provides important information for assessing L2 prosody. For L2 learners, the first step of learning prosody is to put accents or stresses on appropriate syllables in words. A syllable with a stress should be produced longer and one without a stress should be produced shorter. To achieve this, we propose taking a duration ratio for every pair of consecutive vowels in reference to duration contrast of the same vowel pair produced by native speakers. Furthermore, we propose a weighted mean of the ratios on a logarithmic scale in consideration of local importance within a word. In evaluation with English word utterances produced by Japanese learners, the introduction of the weighted mean of the ratio significantly improved the correlation coefficient with subjective scores.