The Maxon AF-9 Auto Filter is an analog envelope follower pedal that creates an automatic wah effect based on the player's pick attack. Like the one of the most coveted early auto-wah pedals, the Mutron III, the AF-9 creates its effect via a CdS Photocoupler rather than a VCA, giving it a warm, vowel-like filtering that cannot be reproduced with cheaper components. Features high, band and low pass filter modes, switchable filter direction and two frequency ranges, with adjustable resonance and sensitivity.