Channel-effect-cancellation method for speech recognition over telephone systems

The performance degradation of speech recognition in telephone systems is due to the additive noise and the filtering effect of telephone channels. The authors propose a probabilistic technique to overcome the filtering effect in telephone systems. A set of reference filters, represented in terms of the cepstrum, is generated by clustering the cepstra of inverse telephone channels. A channel-effect-cancellation filter is then approximated by the convex combination of these reference filters. The convex combination coefficients are automatically determined according to the accumulated observation probabilities when a test utterance passes through the reference filters. The experiments on speech through telephone channels show that the channel effect can be mostly cancelled, and the recognition performance can be significantly improved