TL;DW: Chebyshev filter adds harmonics.
Here’s a nice one! Pafnuty has been much sought after, from back when it only existed as an Audio Unit. Now it’s up to date, in a new more-approachable form, and it’s VST and open source and dithered to the floating-point buss: all the good modern stuff from current Airwindows.
Pafnuty is a Chebyshev filter. What are those? Well, it’s not much like your usual filter: you don’t use this to roll off highs or lows (though under some conditions you might be able to do any of those things). A Chebyshev filter is like a mathematical formula. It works like this: if you feed it a sine wave (at exactly 0dB, or barely-clipping) it can generate entirely new sine waves to add to your sine wave. Which ones? Harmonically related ones. You can have twice, three, four times the frequency, all the way up to thirteenth harmonic.
Pafnuty’s been rearranged in such a way that when you move the sliders to the right, the harmonics add. (The old version used simpler math but gave a slightly weirder arrangement: you’d have to do 1.0 third harmonic, -1.0 fifth, 1.0 seventh and so on for them to add up in phase.) There’s also an attenuverter (which is what you get with a dry-wet control when it also allows for inverse-dry-wet: something out of Eurorack-land, which also existed on the Delta Labs Effectron. Side note about the funky old Effectron: it’s a delta-sigma converter like SACDs but cruder, and I’d been wanting someone to make a DIY-able delay like that. It exists! The Princeton PT2399 chip, which is in lots of current synths and pedals such as the Dreadbox Erebus)
Back to Pafnuty. What do you get when you run music into this sine-multiplying filter? If your audio has no frequencies that, multiplied, go higher than the sampling rate, you get perfect aliasing-free harmonic enhancement. The way the filter works, it absolutely doesn’t generate anything higher than the multipliers it works with. It’s a sort of color-adding harmonic enhancement where you can pick what kind of coloration you add (or subtract, since all the controls go both ways). If the frequencies do go higher than the sampling rate then they do alias, but the way Pafnuty resists adding extra harmonics helps it to resist aliasing and if you don’t add lots of higher harmonics you can go very high in frequency, cleanly.
This might not be the easiest plugin to come to terms with, but it makes a great secret weapon, and produces tones that don’t exist in more normal tone shapers! I hope you like it.
I also hope you don’t literally keep this stuff a secret: my work is supported by Patreon and that’s why I’m still around to make plugins like this (and update hundreds of plugins when the need arises, but that was LAST week). You can’t run around proclaiming the hype of Airwindows Apotheosis as that only backfires, but much like you can share riffs and patches and exchange ideas with people, it’s still possible to get the word out. You gotta do as I do and not lead with hitting people up for money: maybe they don’t have any, and need your and my help. But there are still people who would be able to buy plugins, and anyone who would have bought Pafnuty at $50 could jump on the Patreon for that much a year, either now or later when they’re convinced and are using it in their mixes as a key tone-shaping element.
It also encourages letting people have plugins that don’t phone home, turn themselves off, explode or send all your data to a secret laboratory. Airwindows stuff is open source and has no code of any kind to mess with you: it’s so simple you could learn how to code for audio by looking at it, and on some Mondays we do just that on my livestream. Come and see!