Low complexity, high accuracy clustering method for speech recognizer

Abstract

The clustering technique produces a low complexity and yet high accuracy speech representation for use with speech recognizers. The task database comprising the test speech to be modeled is segmented into subword units such as phonemes and labeled to indicate each phoneme in its left and right context (triphones). Hidden Markov Models are constructed for each context-independent phoneme and trained. Then the center states are tied for all phonemes of the same class. Triphones are trained and all poorly-trained models are eliminated by merging their training data with the nearest well-trained model using a weighted divergence computation to ascertain distance. Before merging, the threshold for each class is adjusted until the number of good models for each phoneme class is within predetermined upper and lower limits. Finally, if desired, the number of mixture components used to represent each model may be increased and the models retrained. This latter step increases the accuracy.