Yes changing those filter cap values would shift the entire response. But my point was that the swing of the circuit as it stands is quite extreme. In auto mode when there is no input signal the filter sweeps to a very low frequency. In fact I'm not sure if it doesn't close down completely all the way to DC. Then when you do have an input signal and you increase the sensitivity the filter opens up to a relatively high frequency.
What might be more useful is an offset control which allows you to set the bottom rest frequency of the filter.
I just build my Envelope Filter last night... it took me an hour or so to build and 5 to tweak hehehe. I have found that I definitely want the concept you describe above Tark. I did make changes to all of the film cap values (thankfully I knew I was going to want this and socketed them all during the build). Here's what I ended up with (caviat - I'm doing it all from memory at the moment, and I changed these so many times last night I'm not 100% certain but I believe these to be correct)
Env Filter Cap changes.jpg [ 144.09 KB | Viewed 575 times ]
This gave me a smoother filter tone (most especially the .01uF at the top) so that the effect is much more subtle (less in-your-face, considerably less tinny at the top of the sweep). Another change that I made was to swap out the 4558 OpAmp for the Burr Brown Hi-Fi one (I have a habit of this change in most of my pedals) and the tone of the effect seems cleaner, more crystalline (Hi-Fi, in truth). After swapping, re-swapping, un-swapping, and finally settling on the caps listed in the picture (90% certain - I'll verify when I get a chance) I still foudn that the bottom end of the sweep essentially functions as a gate effect, which is a fun effect in its own right, but as I tend to use my Envelope Filter somewhat regularly (currently have a Riddle: Q-balls - which I intend to replace with the BYOC Env Filter, for a lot of reasons:standard power source, footprint, and the fact that the Q-balls adds a huge signal boost when active) I need for some signal to pass through even at a lower volume. The compressor helps certainly, but it also pushes the attack of the filter, and thereby the sweep ranges above where I want it.
Ideally, I want that gate effect to allow pass through of even low volumes, and the the hardest strikes to remain in the range of a pleasant tone, rather than pushing the signal up into the brash tweet range. I got the high end dialed in with the changes above, but still have the low end gate to tackle.
Needless to say, like all of my BYOC pedals, I love this one and will probably continue to futz with it forever hehehe.
Anyone have an idea what part of the signal path is pushing the low end so far down that it effectively becomes a gate? I'll find it eventually (hopefully with wrecking anything), but if someone can point me at a component to swap, I'd appreciate it.
Also finished my Pickled Beaver, and Octave Fuzz this week, and needless to say, I have lots and lots of new tone to play with for a while.