Single-tree method for grammar-directed search

We present a very fast and accurate fast-match algorithm which, when followed by a regular beam search restricted within only the subset of words selected by the fast-match, can speed up the recognition process by at least two orders of magnitude in comparison to a typical single-pass speech recognizer utilizing the Viterbi (or beam) search algorithm. In this search strategy, the recognition vocabulary is structured as a single phonetic tree in the fast-match pass. The search on this phonetic tree is a variation of the Viterbi algorithm. Especially, we are able to use a word bigram language model without making copies of the tree during the search. This is a novel fast-match algorithm that has two important properties: high-accuracy recognition and run-time proportional to only the cube root of the vocabulary size.