Electro-Harmonix Knockout Attack EQ Controls: Low, Dry, High.1/4" input and outputDC power input for battery replacement.LED indicates whether effect is engaged or bypassed. Two powerful filters are the key -- make your humbuckers sound like single coil pickups and your Strat sound like a Tele Amazing on bass!The Knockout Attack Equallizer lets you tweak the high-pass and low-pass filters, changing your sound from Gibson to Strat to Telecaster, with innumerable shades in between