Keeley Neutrino Envelope Filter and Auto-Wah! This funky, tripped-out circuit is something I’ve wanted to do for over a decade. Reviews have been stellar. Each opto-coupler is tuned to perfection; every Keeley Neutrino is like finding a magical vintage unit with that perfect tone. The Keeley Neutrino gives you all the classic, funk, auto-wah sounds and that Jerry-In-A-Box sound. We have used the classic opto-coupler design for a rich and warm depth to the effect. Envelope filter sound is an effect triggered by your pick attack or strength. The harder you pick, the harder it “wahs”! Sounds bubble up from a deep rounded warmth to a shining brilliance. Solo notes are individually expressive based on how hard you play. Create incredible vowel sounds.