If you're in the market for bottomless sub-octave possibilities in a compact package, the Electro-Harmonix Octave Multiplexer is knocking at your door. The pedal's ability to drop any monophonic signal an octave makes this pedal ideal for solo artists looking for a fuller sound, experimental music, and wild bass sounds from virtually any instrument. This pedal bas been produced in both an older box larger format, as well as a smaller more recent enclosure which is sometimes referred to as the XO version.