In Bandoneonbook (2003) by Hans W. Koch the acoustic feedback between the small, internal microphone and the loudspeaker of a computer is played by opening and closing the laptop, similar to how one would play a bandoneon. The music software, Max (at that time, still MaxMSP), is controlled by the keyboard of the laptop. By pressing some keys the feedback is filtered in different ways. A piece which can only be performed with the titanium PowerBook series of 2001!