Nortel Networks Corporation

Andre Gillet

Vishwa N Gupta

Peter R Stubley

Serge Robillard

David Bruce Peters

Waleed Fakhr

Christopher K Toulson

Nadia Girolamo

Speech recognition systems and methods consistent with the present invention process input speech signals organized into a series of frames. The input speech signal is decimated to select K frames out of every L frames of the input speech signal according to a decimation rate K/L. A first set of model distances is then calculated for each of the K selected frames of the input speech signal, and a Hidden Markov Model (HMM) topology of a first set of models is reduced according to the decimation rate K/L. The system then selects a reduced set of model distances from the computed first set of model distances according to the reduced HMM topology and selects a first plurality of candidate choices for recognition according to the reduced set of model distances. A second set of model distances is computed, using a second set of models, for a second plurality of candidate choices, wherein the second plurality of candidate choices correspond to at least a subset of the first plurality of candidate choices. The second plurality of candidate choices are rescored using the second set of model distances, and a recognition result is selected from the second plurality of candidate choices according to the rescored second plurality of candidate choices.

Search and rescoring method for a speech recognition system

Comparing a series of observations representing unknown speech, to stored models representing known speech, the series of observations being divided into at least two blocks each comprising two or more of the observations, is carried out in an order which makes better use of memory. First, the observations in one of the blocks are compared (31), to a subset comprising one or more of the models, to determine a likelihood of a match to each of the one or more models. This step is repeated (33) for models other than those in the subset; and the whole process is repeated (34) for each block.

Method and apparatus for speech recognition

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St-Laurent, Canada

Andre Gillet