MXR's 18 volt Constant Headroom Technology provides high headroom and superior tracking. Use the Dry knob to mix in your direct signal and hit the Mid+ switch to add up to +14dB of internally adjustable mid frequencies (400Hz or 850Hz). Finally, mix in two separately controlled octave voices - Growl (for throaty tone) and Girth (for deep tone). The MXR Bass Octave Deluxe is powered by Dunlop's ECB003 AC Adapter or single 9 volt battery.