Look-ahead techniques for fast beam search

This paper presents two look-ahead techniques for speeding up large vocabulary continuous speech recognition. These two techniques are the language model look-ahead and the phoneme look-ahead; both are incorporated into the pruning process of the time-synchronous one-pass beam search algorithm. The search algorithm is based on a tree-organized pronunciation lexicon in connection with a bigram language model. Both look-ahead techniques have been tested on the 20 000-word NAB’94 task (ARPA North American Business Corpus). The recognition experiments show that the combination of bigram language model look-ahead and phoneme look-ahead reduces the size of search space by a factor of about 30 and the computational effort by a factor of 5 without affecting the word recognition accuracy in comparison with no look-ahead pruning technique.