6. A computer-implemented method, comprising: under control of one or more computing devices configured with specific computer-executable instructions, receiving an utterance; generating an input finite state transducer (FST) comprising sequences of subword units organized into input FST paths, wherein a path of the input FST paths corresponds to a speech recognition hypothesis of a plurality of speech recognition hypotheses that are based on the received utterance; obtaining a grammar of utterances, wherein each utterance of the grammar of utterances comprises a sequence of subword units; generating, using the grammar of utterances, an utterance FST comprising sequences of subword units organized into utterance FST paths, wherein a path of the utterance FST paths corresponds to a command; generating an output FST using the input FST and the utterance FST, wherein the output FST comprises a first path indicative of a difference between a first path of the input FST paths and a first path of the utterance FST paths, and a second path indicative of a difference between the first path of the input FST paths and a second path of the utterance FST paths; computing a first difference score using the first path of the output FST; computing a second difference score using the second path of the output FST; and determining a first command representative of the received utterance based at least in part on the first difference score and the second difference score.
6. A computer-implemented method, comprising: under control of one or more computing devices configured with specific computer-executable instructions, receiving an utterance; generating an input finite state transducer (FST) comprising sequences of subword units organized into input FST paths, wherein a path of the input FST paths corresponds to a speech recognition hypothesis of a plurality of speech recognition hypotheses that are based on the received utterance; obtaining a grammar of utterances, wherein each utterance of the grammar of utterances comprises a sequence of subword units; generating, using the grammar of utterances, an utterance FST comprising sequences of subword units organized into utterance FST paths, wherein a path of the utterance FST paths corresponds to a command; generating an output FST using the input FST and the utterance FST, wherein the output FST comprises a first path indicative of a difference between a first path of the input FST paths and a first path of the utterance FST paths, and a second path indicative of a difference between the first path of the input FST paths and a second path of the utterance FST paths; computing a first difference score using the first path of the output FST; computing a second difference score using the second path of the output FST; and determining a first command representative of the received utterance based at least in part on the first difference score and the second difference score. 13. The method of claim 6 , wherein said generating an output FST using the input FST and the utterance FST further comprises generating an edit FST based at least in part on a subword unit confusion table.