Method for processing an original time-domain digital audio signal in which said signal is split into a plurality of narrow-band time-domain digital audio signals confined to specific frequency bands, short-term segments of which are temporarily stored in memory, - having signal processing algorithms for extracting from said segments of said narrow-band time-domain signals, in a fixed sequence or upon request from a decision-making algorithm, narrow-band time-domain features such as accumulated energy in each band, average amplitude, variances, maximal and minimal amplitudes, local maxima and minima, envelopes, parameters of polynomial approximations, interpolated values, statistics of distances between observed and calculated zero-crossings, - having said decision-making algorithm make tentative or final decisions about the type of occupancy of frequency bands resulting from said narrow-band time-domain features, - having said decision-making algorithm request from said signal processing algorithms further specific feature extractions from specific short-term segments and make tentative or final decisions about the type of occupancy of frequency bands resulting from the requested features, - having said decision-making algorithm store its tentative and final decisions about band occupancy for processing together with results from later short-term segments, - and having said decision-making algorithm output final decisions derived from current and past short-segments in the form of a set of notes having been played over some recent time interval, together with information relating to the timing of each note from the set, characterised in that - said decision making also stores ongoing segments, features and/or decisions and extracts from them information referring specifically to the current instrument and its current tuning. - having signal processing algorithms for extracting from said segments of said narrow-band time-domain signals, in a fixed sequence or upon request from a decision-making algorithm, narrow-band time-domain features such as accumulated energy in each band, average amplitude, variances, maximal and minimal amplitudes, local maxima and minima, envelopes, parameters of polynomial approximations, interpolated values, statistics of distances between observed and calculated zero-crossings, - having said decision-making algorithm make tentative or final decisions about the type of occupancy of frequency bands resulting from said narrow-band time-domain features, - having said decision-making algorithm request from said signal processing algorithms further specific feature extractions from specific short-term segments and make tentative or final decisions about the type of occupancy of frequency bands resulting from the requested features, - having said decision-making algorithm store its tentative and final decisions about band occupancy for processing together with results from later short-term segments, - and having said decision-making algorithm output final decisions derived from current and past short-segments in the form of a set of notes having been played over some recent time interval, together with information relating to the timing of each note from the set, characterised in that - said decision making also stores ongoing segments, features and/or decisions and extracts from them information referring specifically to the current instrument and its current tuning.