Segment-Synchronization Problem in Speech Recognition

Procedures for the segmentation of acoustic continuum of speech cannot usually guarantee that two utterances of the same phrase by the same speaker will always result in the same number of segments even under ideal conditions. To match the segmental parameters of an utterance against known parameters of the same phrase, one must determine correspondences between the segments of the two utterances. A solution to this synchronization problem that requires no time normalization can be based on the possibility labeling the segments at least in terms of phoneme groups. Segments of unvoiced fricatives and vowels can usually be more reliably detected than others. Therefore, the synchronization procedure first maps vowel to vowel and fricative to fricative. The few unmapped segments between any two pairs can then be mapped using segment labels such as nasal or stop, or on the basis of similarity of segmental parameters. This scheme is much faster than correlation-based schemes and has been used successfully in a real time recognition program. It took 4 (15) sec/recognition for a 50-(500)-word vocabulary to achieve 98% correct recognition.