Like the legendary Big Muff Pi of the ’70s, the reissue Electro-Harmonix USA Big Muff Pi Distortion/Sustainer Pedal has 3 controls that let you dial in the finest harmonic distortion/sustain ever produced. The Volume control adjusts the output level. The Sustain control optimizes the long sustain with just the right amount of harmonic distortion. The Tone control provides a range of sounds, from warm bass to crisp treble.