TL;DW: Biquad2 is the Airwindows biquad filter that’s more sweepable and synthy.

This time, it’s time for the impossible!

As in, there was a reason nobody was doing sweepable, ‘synthy’ biquad filters…

Turns out it simply doesn’t work. One uses a different type, like state variable filters, for the synthy stuff. The reason is that, while biquads can sound pretty great (especially implemented like I do ’em), they fundamentally can’t cope with changing the filter coefficients mid-calculation. They flip out: you’ll hear some of that, especially at the frequency extremes. Low Q makes low frequency motions flip out, and high Q (and boy do I have a high Q for you this time) makes ultra-high frequency motions flip out in a really wild. glitchy way.

So obviously I gave up.


nope! Instead, I just kind of forced the filter into zones where it mostly is controllable. This is partly through REALLY smoothing the filter cutoff, especially at low Q and low frequencies. If you try and update biquad coefficients every sample (and I already changed the form from the more CPU-efficient to the more stable form: didn’t help much at all) the algorithm gets super twitchy, so part of what I’ve done is just stabilizing things. I tried for ages to come up with some bizarre hack to force the filter back into stability: no dice. So, the range has been limited a little, the Q doesn’t adjust below a Q of 1, and it reacts really slowly, because that was the only way I could get it to behave at all. (the original Biquad can sometimes be better behaved, because it’s only recalculating coefficients every new buffer. So, zipper noise. When you get rid of that your troubles get infinitely worse, with biquads)

I’ve also got the resonance (on low and highpass) working differently. I’m scaling back loudness, but I’m also applying a distortion, then averaging after that, to try and get an ‘overdriving filter effect’ not present in the purer original Biquad. You can go quieter into Biquad2 and avoid this, or not use as much resonance: I feel it’s kind of like the Roland Alpha Juno filter resonance distortion, not an everyday thing but when it pops up it has its own distinct quality that’s interesting.

Anyway here’s Biquad2 ;)

Patreon is how I’m able to stick around doing this stuff, and/or fixing up stuff that needed fixing. It’s become clear from the response to Monitoring (yes, I’ve got an update coming) that among the things that need fixing are ‘you make too many plugins!’ Since I can’t go and throw most of ’em away, I’ll need to do two further things: one, do more ‘combination’ plugins such as one that includes the MANY Airwindows distortion and saturation types. Two, come up with ‘sets’ of starter plugins meant to work together, which may include custom versions of plugins like Console, and three, get some more building blocks like basic EQs out there. Whoops, that’s more than two :) anyway, even if I can’t design a DAW directly, I ought to be able to tailor versions of Console and tone shapers and channel strip parts together and produce cohesive sets of plugins that are waaaay more approachable to the Airwindows neophyte. Since MV, I’d also like to do reverbs and really get a whole tapestry of mixing together.

We shall see. Enjoy the sweep-ier biquads :)