The invention enables to generate a general function (4) which can operate on an input signal (Sx) to extract from the latter a value (DVex) of a global characteristic value expressing a feature (De) of the information conveyed by that signal.It operates by: generating at least one compound function (CF1-CFn), said compound function being generated from at least one of a set of elementary functions (EF1, EF2, . . . ) by considering the elementary functions as symbolic objects, operating said compound function on at least one reference signal (S1-Sm) having a pre-attributed global characteristic value (Dgt1-Dgtm) serving for evaluation, by processing (22, 27) the elementary functions as executable operators, determining the matching between: i) the value(s) (Dij) extracted by said compound function as a result of operating on said reference signal and, ii) the pre-attributed global characteristic value (Dgt1-Dgtm) of said reference signal, and selecting at least one compound function on the basis of the matching to produce the general extraction function. The invention can be used, for instance, for the automatic extraction of audio/music descriptors from their signals contained as music file data.