The Proton Mk IV Envelope Filter

By Scott Ulrichs · Vol. 26, No. 5 · March 2025

Spencer Doren of 3 Leaf Audio talks about the evolution of his Proton envelope filter — a Mu-Tron III–inspired design now in its fourth version — along with his Octabvre, Doom 2, and the philosophy behind running a thriving boutique pedal company without social media.

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