11. A computer-readable storage device storing computer-executable instructions that, when executed, cause one or more processors to perform acts comprising: converting a plurality of feature vectors into a plurality of log probability sets using a classifier ensemble that includes a plurality of classifiers, the plurality of feature vectors representing a speech utterance; transforming the plurality of log probability sets into a plurality of output symbol sequences using a decoder ensemble that includes a plurality of decoders; combining the plurality of output symbol sequences into a fusion output symbol sequence using a block fusion algorithm, the block fusion algorithm to use convergent iterative a-priori probability calculations to produce the fusion output sequence; and retrieving one or more stored speech utterances from a speech database based on at least one of the plurality of output symbol sequences or the fusion output symbol sequence.
14. The computer-readable storage device of claim 11 , wherein the converting includes using a classifier ensemble that comprises at least two classifiers having different sets of classification classes, and wherein the output symbol sequences produced by the at least two classifiers include symbols that cover different durations within the speech utterance.