Pigtronix Resotron is an analog filter that brings the sound of 70’s keyboard synthesizers to the world of envelope pedals for guitar, bass and beyond. The filter at the heart of the Resotron is based on the SSM2040 chip found in the legendary Prophet 5 and Octave CAT synthesizers. This 24db/octave, the state-variable filter provides the full gamut of familiar envelope filter sounds with UP and DOWN sweeping modes, and a sensitivity control to dial in the response of the effect based on how hard you play.