1. A method comprising: receiving an unknown utterance; generating a first sequence of feature vectors from the unknown utterance; removing, in a first recognition pass and using a parameter, at least a portion of irrelevant information from the first sequence of feature vectors resulting in a second sequence of feature vectors; recognizing speech in the first recognition pass based at least in part on the second sequence of feature vectors to obtain a first result; updating the parameter used in the removing based at least in part on the first result; removing, in a second recognition pass, using the updated parameter, at least a portion of irrelevant information from the first sequence of feature vectors resulting in a third sequence of feature vectors; and recognizing speech in the second recognition pass based at least in part on the third sequence of feature vectors to determine a second result.