7. A system comprising: one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising: selecting a candidate portion of a language model to evaluate for pruning; obtaining an entropy score representing information loss that would result from pruning the candidate portion of the language model; obtaining an acoustic score representing acoustic confusability of one or more words modeled by the candidate portion of the language model; evaluating whether to prune the candidate portion of the language model using the entropy score and the acoustic score; and generating a pruned language model based on pruning the candidate portion from the language model; and generating, by a speech recognizer using the pruned language model, a transcription of an utterance.
7. A system comprising: one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising: selecting a candidate portion of a language model to evaluate for pruning; obtaining an entropy score representing information loss that would result from pruning the candidate portion of the language model; obtaining an acoustic score representing acoustic confusability of one or more words modeled by the candidate portion of the language model; evaluating whether to prune the candidate portion of the language model using the entropy score and the acoustic score; and generating a pruned language model based on pruning the candidate portion from the language model; and generating, by a speech recognizer using the pruned language model, a transcription of an utterance. 8. The system of claim 7 , wherein the language model includes sequences of contiguous items and the candidate portion includes a sequence of contiguous items.