Electro-Harmonix BASS BIG MUFF Pi Distortion/Sustain PedalThe Bass Big Muff Pi Distortion Sustain Pedal from Electro Harmonix is a harmonic distortion sustain device for the electric bass guitar. The pedal is based on the Russian battle tank green Sovtek Big Muff Pi from the late '90s, and the original Electro Harmonix Big Muff Pi from the early '70s. You can use the unit to thicken up your sound, or give it a low end growl. A bass boost EQ switch reintroduces your low frequencies when tone is set for high