5. The method of claim 1 wherein using the query term to retrieve a document identifier and a position identifier comprises comparing a term confidence level to word scores associated with occurrences of the query term in the index and retrieving document identifiers and position identifiers that are associated with word scores that exceed the term confidence level, wherein the word scores are based on probabilities of phonetic units given feature vectors formed from the audio signal.
5. The method of claim 1 wherein using the query term to retrieve a document identifier and a position identifier comprises comparing a term confidence level to word scores associated with occurrences of the query term in the index and retrieving document identifiers and position identifiers that are associated with word scores that exceed the term confidence level, wherein the word scores are based on probabilities of phonetic units given feature vectors formed from the audio signal. 6. The method of claim 5 further comprising: determining that the query term comprises a combination of two query words; and increasing the word scores retrieved from the index for occurrences of the query term before comparing the word scores to the term confidence level.