Actually, a self contained MIDI arpeggiator that actually works has been done... Waldorf Gekko anyone? http://matrixsynth.blogspot.com/2008/01/waldorf-gekko-midi-arpeggiator.html I have the Waldorf Chord Gekko which adds a chord memory function to any keyboard. Extrememely useful, and brilliant one-button, one LED interface. Sam E.