TL;DW: BiquadDouble is a handy Airwindows cascaded biquad filter: steeper roll-off before resonance.

Here’s another utility plugin! Some weeks it’s nice to be boring (for those reading this in the future, check the date: these are regrettably ‘interesting times’ where I live, most likely historically so)

So it’s a boring old biquad.

Except, if you’re into the details of how stuff works, it’s not THAT boring. It’s two biquad filters stacked, which means you can get twice as much cutoff steepness before resonance. Since it’s Airwindows, you can have any possible resonance setting anyway, from ‘impossibly high’ to so wide that it’s basically full bandwidth. That interacts interestingly with the stacked filters: some of the weird effects with super-wide filters will act different here. On top of that, it’s two stacked filters inside an internal Console mixing system: so the tone of the filter itself is ‘expanded’ in a way not common to boring old biquad filters. And it’s the most efficient (but least cooperative) biquad, meaning that it runs and sounds great but doesn’t always cooperate with rapid automation, so that might get interesting if you’re not careful.

Why do this at all?

Because I sometimes like mocking up effects and plugins out of component parts. And if I was to use a stacked biquad filter as part of something else, it’s just more convenient to dial in the correct settings and get the tone exactly right: I could use two ‘Biquad’ instances, but remember that BiquadDouble stacks its filters INSIDE the Console processing, so it might not be as good to fake it, plus I’d have to set both the Biquad instances the same…

The real answer is ‘because that’s how I roll’. Nobody asked for this. But maybe you reach for a biquad filter for simple tone shaping, and you keep trying to find a butter zone between too shallow, and too resonant. This might become your go-to basic filter. I can’t predict what will take off: for all I know, this is THE basic digital filter everyone’s been waiting for, the one that just sounds right for every purpose. Or not. But you can’t know until you try :)

If I just made your silver bullet EQ (stranger things have happened) without even meaning to, by all means go to my Patreon and kick in an additional $50 a year. Or not, if you’d rather not. I never can tell what people will get super excited over, but the nice thing about relying on Patreon is that I don’t have to stick to only what I think will excite people or sell units. I can throw out a weird (or boring) experiment, that to me seems like no big deal, and if people love it then hey! It’s yours.

Side note for coders: one of the reasons I’ve done BiquadDouble is to make it easy to add a stacked biquad of specific design to my, or your, code. So part of what this plugin is, is the code base on Github. It’s MIT license, you only have to credit Airwindows and you can use both my implementation and the Console code that wraps it. Might help you get a richer, deeper tone color than your plugin rivals :)