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Single tree method for grammar directed, very large vocabulary speech recognizer

  • US 5,621,859 A
  • Filed: 01/19/1994
  • Issued: 04/15/1997
  • Est. Priority Date: 01/19/1994
  • Status: Expired due to Term
First Claim
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1. A method of recognizing a word as being one of a plurality of words in a vocabulary, the method comprising the steps of:

  • constructing a phonetic tree having a plurality of branches, a phoneme being associated with each branch, a phonetic HMM being associated with each branch so as to model the phoneme, and a word being associated with the end of a sequence of branches, such that all words that include the same initial phoneme sequence include the same initial branches in the phonetic tree, each branch having a left-context consisting of no more than a single branch, and each branch other than final phonemes of a word having a right-context that includes at least one branch;

    compiling a statistical language model having a plurality of grammar states and transition probabilities between grammar states, each grammar state including at least one word;

    associating with each branch a set of common-phoneme words, each common-phoneme word including the phoneme associated with the branch;

    computing, for each set of common-phoneme words and for each preceding grammar state that precedes the set of common-phoneme words, a set transition probability that is a function of the transition probabilities from the preceding grammar state to each common-phoneme word of the set; and

    upon entering a branch, determining which preceding grammar state of a plurality of preceding grammar states is most likely to transition into a common-phoneme word of the set of common-phoneme words associated with the branch.

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