Continuous Recognition of Large-Vocabulary TelephoneQuality Speech

The problem of speech recognition over telephone lines is growing in importance, as many near-term applications of spoken-language processing are likely to involve telephone speech. This paper describes recent efforts by the CMU speech group to improve the recognition accuracy of telephone-channel speech, particularly in the context of the 1994 ARPA common Hub 2 evaluation of speech over long-distance telephone lines. The greatest amount of work was directed toward determining a training procedure that provides the greatest recognition accuracy when the incoming speech is known to be collected over the telephone. We compare the effectiveness of three training procedures, finding that training using high-quality speech that is bandlimited to 8 kHz can achieve results that are as good as those obtained by training on speech of a similar bandwidth collected over actual telephone channels. We also compare the recognition accuracy of the SPHINX-II system using high-quality speech and telephone speech, and we comment on the reasons for differences in system performance. 1