First things first... this is the build guide for this module.
You've found the blog post for the OctoPass. It's an eight-channel high-pass fixed-frequency four-pole filter (alliteration!) that is a requested build. It's switchable -- there's little toggle switches on the panel that will allow the user to low-cut or not the signal.
The signal switching is done with a ton of Vactrols -- LED and LDR combos. This means very-low-noise, which may be important if you're deciding to cascade all 8 filters with all the normalling going on between all eight channels.
The build is a bit fiddly, with some pads quite close together. Use a sharp soldering iron tip, cleaned frequently, lead-bearing solder if legal, flux if necessary, and double-triple check all your joints. I did have some dry solder joints on some of the op amp legs, but besides that, all four of these I built worked just fine.
