1. A method of processing an input signal representing a spoken utterance, the spoken utterance having a key utterance component and an extraneous sound component, the method comprising the steps of comparing the input signal to a plurality of speech recognition models within a speech recognition system, said plurality of speech recognition models including key word speech recognition models representative of respective different key utterances and further including at least a first sink model, and recognizing a particular one of said key utterances in said spoken utterance in response to said comparing, characterized in that said sink model represents a plurality of extraneous sound training tokens, at least two of said extraneous sound training tokens being other than repetitions of a particular one vocabulary item.