Speech-adaptive time-scale modification for computer assisted language-learning

In traditional foreign language learning programmes students are offered a tutor model characterised by slow, deliberate speech. This is insufficient to prepare them to cope with native, colloquial speech. By applying a time-scale modification (TSM) algorithm to natural-speed, native speech, students have access to a more desirable, natural speech corpus which permits them to practise essential listening skills in a more focussed manner. We present a method which allows slowing down speech without compromising the quality, pitch or naturalness of the slowed speech by applying different scaling factors to different types of speech segments. The new method is compared to traditional uniform-rate techniques and other variable time-scaling methods. The results show that the proposed approach produces a superior quality output, even for high modification rates.