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.