"Current releases of Audacity are now slowly adding support for MIDI. As of October 2008, MIDI files can be imported, cut-and-paste edited, then exported as MIDI. However this feature is still buggy, and there is no MIDI playback. "
http://wiki.audacityteam.org/wiki/MidiПишут что это баг. Вставить МИДИ можно, а с воспроизведением - проблемы! Не знаю на сколько актуальна данная статья...