I've done my research and it seems like mutron-style envelope filters seem to be well loved on TB. I've been following this brand called VFE for a while (if I could afford it now I'd get their Alpha Dog in a heartbeat), and I noticed this: http://www.vfepedals.com/projects.html This is a page listing Peter's brainstorming ideas and works in progress, and under the "Project List" tab, I think a lot of people would be interested in his Mini Mu. Here's a picture and the info from the website: The first edition of the Mini Mu is a simple clone of the classic Mutron III envelope filter (aka autowah). A few extras have been added, namely a passive output level attenuator and an "in between" position on the range switch. With the included charge pump, this runs on +/-9V like the original without needing a special power supply or two batteries. Subscribe for Mini Mu Updates GAIN: Controls the pre-gain of the circuit, and affects how the circuit responds to the dynamics of the input signal. PEAK: Controls the amount of resonant feedback in the filter. LEVEL: Passive attenuator to adjust the output volume. DRIVE: Selects between a upward frequency sweep & a downward frequency sweep. RANGE: Selects between a higher or lower frequency sweep range. MODE: Selects, between high pass, band pass, and low pass modes. INTERNAL CONTROL: The internal trimpot affects how the LDRs respond to the trigger circuit. This greatly affects the sweep & feel of the filter sweep. To give an idea of more things he does, here's a demo of the Alpha Dog, Pale Horse, White Horse, Blueprint, and Bumblebee, and here's a demo of the Pale Horse, Old School, and Alpha Dog. A side note: on the projects page, if you go to brainstorming, you can see some more ideas he has. The bass octave fuzz looks delectable.