1. A method of generating a footprint for an input useful signal, wherein the input useful signal represents a spectrum of useful signal frequencies over time, comprising the steps of: processing at least one data set representing a part of the input useful signal with an analyzer according to a predetermined analyzing instruction to generate a useful signal vector; providing a pattern directory of a plurality of pattern vectors each having a unique associated pattern number not being a vector; comparing the useful signal vector with each of the pattern vectors in the pattern directory; determining the associated pattern number of a one of the pattern vectors having a highest similarity with the useful signal vector; and generating a footprint of the input useful signal with the determined pattern number as at least a portion of the footprint of the input useful signal.