A significant short-time spectrum is extracted from an information signal, the means for extracting being configured to extract such short-time spectra which come closer to a specific characteristic than others. The short-time spectra extracted are then decomposed into component signals using ICA analysis, a component signal spectrum representing a profile spectrum of a tone source which generates a tone corresponding to the characteristic sought. From a sequence of short-time spectra of the information signal and from the profile spectra determined, an amplitude envelope is calculated for each profile spectrum to indicate how a tone source profile spectrum changes over time. The profile spectra and all the amplitude envelopes associated therewith provide a description of the information signal which may be evaluated further, for example for transcription purposes in the case of a music signal.