Electro-Harmonix Micro POG octave pedal
Become each member of the violin family on just one instrument! The MICRO POG (Polyphonic Octave Generator) delivers perfect tracking and smooth polyphony for string players. Play an octave above or below (violinist becomes violist or cellist, cellist becomes violist or bassist, bassist becomes cellist, etc.) or play octaves in parallel for a unique effect that is otherwise difficult to execute in tune on stringed instruments!