Spent some time tweaking filter curves for HiLoFilter, using the same polynomial interpolation trick I wrote about previously. Grapher is such a neat tool, but unfortunately it's soooo buggy. Oh well, once I get the formulas right, I won't need it anymore.
HiLoFilter is much more usable now, the curves are more performance oriented and give a bit more wiggle room where it matters. That is to say, on the high-pass filter, the curve lets the user select the lower frequency more precisely (and vise-versa). In the process, I've also reduced some of the clicking that HiLoFilter produces when shifting filter state, but unfortunately it's not completely eliminated. I'll need a lot more debugging time to figure out exactly why that is happening, because it's definitely there but not much harder to reproduce.