1. A method of extracting classifying data from an audio signal, the method comprising the steps of: (a) processing said audio signal into a perceptual representation of its constituent frequencies; (b) processing said perceptual representation into at least one learning representation of said audio data stream; (c) inputting at least one said learning representation into a multi-stage classifier, whereby said multi-stage classifier extracts classifying data from said learning representations and outputs the classification of said audio signal.