Intonation evaluation of English utterances using synthesized speech for Computer-Assisted Language Learning

In this paper, we describe a system for intonation evaluation of English utterance by Japanese native speakers using synthesized speech for rapid development of a CALL system. To evaluate the intonation of learners' utterance, we need reference utterances, for which English native speakers' utterances should be used. However, it is costly to gather native speakers' utterances for all sentences in the system. Therefore, we examined an intonation evaluation method using synthesized speech generated by text-to-speech systems instead of real speech. Intonation evaluation system calculates scores between a learner's utterance and corresponding utterances by the teachers. We investigated a method of combining multiple scores. In addition, we incorporated a feature for rhythm evaluation into intonation evaluation. As a result, we obtained improvement of correlation between scores by human evaluators and the system. Furthermore, we analyzed a tendency of intonation evaluation by the system through limiting evaluation utterances to find out what degrades the system performance.