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: accessing a query transcription log; identifying, in the query transcription log, manual corrections of automated speech recognizer generated transcriptions of a particular term; identifying audio samples of speech corresponding to the manual corrections of the automated speech recognizer generated transcriptions of the particular term; obtaining candidate pronunciations for the particular term; generating, for each pair of the candidate pronunciations for the particular term and the audio samples of speech corresponding to the manual corrections of the automated speech recognizer generated transcriptions of the particular term, a score reflecting a level of similarity between the candidate pronunciation of the particular term and the audio sample corresponding to the manual correction of the automated speech recognizer generated transcription of the particular term, wherein the score of the candidate pronunciation for a particular term is obtained by using a minimum of individual scores of phonemes comprising the term; aggregating the scores for each candidate pronunciation; adding two or more candidate pronunciations for the particular term and the respective aggregated scores to a pronunciation lexicon based on the aggregated scores for the candidate pronunciations; and generating a transcription using the two or more candidate pronunciations and respective aggregated scores for the particular term stored in the pronunciation lexicon to recognize an utterance of the particular term.
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: accessing a query transcription log; identifying, in the query transcription log, manual corrections of automated speech recognizer generated transcriptions of a particular term; identifying audio samples of speech corresponding to the manual corrections of the automated speech recognizer generated transcriptions of the particular term; obtaining candidate pronunciations for the particular term; generating, for each pair of the candidate pronunciations for the particular term and the audio samples of speech corresponding to the manual corrections of the automated speech recognizer generated transcriptions of the particular term, a score reflecting a level of similarity between the candidate pronunciation of the particular term and the audio sample corresponding to the manual correction of the automated speech recognizer generated transcription of the particular term, wherein the score of the candidate pronunciation for a particular term is obtained by using a minimum of individual scores of phonemes comprising the term; aggregating the scores for each candidate pronunciation; adding two or more candidate pronunciations for the particular term and the respective aggregated scores to a pronunciation lexicon based on the aggregated scores for the candidate pronunciations; and generating a transcription using the two or more candidate pronunciations and respective aggregated scores for the particular term stored in the pronunciation lexicon to recognize an utterance of the particular term. 8. The system of claim 7 , wherein adding two or more candidate pronunciations for the particular term comprises: identifying a candidate pronunciation of the candidate pronunciations with an aggregated score that indicates a closer level of similarity between the candidate pronunciation and the audio samples than levels of similarity between the other candidate pronunciations and the audio samples; and adding the identified candidate pronunciation to the pronunciation lexicon.