30. The method recited in claim 29 wherein the predetermined level amplitude is a level that corresponds substantially to silence, and said time interval corresponds to the time interval between successive periods of silence in the audio signal.
29. The method recited in claim 28 wherein the signal to be identified includes an audio signal, and wherein the step of extracting the feature string includes the step of monitoring the amplitude of the audio signal and determining the time intervals that the amplitude of the audio signal departs from a predetermined level of amplitude.