Method and apparatus for automatically generating a general extraction function calculable on an input signal, e.g. an audio signal to extract therefrom a predetermined global characteristic value of its contents, e.g. a descriptor

A method implemented by a computer programmed as a signal processing device that generates a general extraction function configured to operate on an input signal to extract therefrom a value of a global characteristic expressing a feature of the information conveyed by that signal, the method comprising:

• generating, by a processor of the computer, a plurality of compound functions, said plurality of compound functions being generated from a library of elementary functions by considering said elementary functions as symbolic objects;
• operating said plurality of compound functions on at least one reference signal having a predetermined global characteristic value serving for evaluation, by processing said elementary functions as executable operators to generate an output value for each compound function;
• determining, for each compound function, a fitness value determined from a fitness function that evaluates a difference between the output value generated by said compound function as a result of operating on said at least one reference signal, and the predetermined global characteristic value of said at least one reference signal;
• and
• selecting a compound function from the plurality of compound functions on the basis of the plurality of fitness values determined in the determining step to produce said general extraction function.