TL;DW: Biquad is the Airwindows implementation of a biquad filter.

Biquad.zip(366k)

This little puppy is really flexible!

That’s true of any biquad filter, but I find most of them are really flexible and slightly plastic. Traditionally biquads require special handling, because you can’t push them too far before they break, and also they sound ‘DAW-y’ and synthetic. Not in the same way as linear-phase EQs, mind you, but still with something about them that feels digital.

So I fixed that :) with a couple caveats. Firstly, part of it is brute force. I figured that if biquads run into trouble with 32-bit coefficients on some filter curves, and it’s widely known that you should do things like run ’em in series to get better behavior, we could always run long doubles and be totally sure they work as intended. Overkill? Meh. Sure, but it’s known that these break due to losing control of themselves due to not long enough wordlengths. Why wouldn’t they work and sound better with long enough wordlengths? And so they do. Also, you get to run simpler biquads if you don’t have to run lots of them, so it averages out. I think it’s just a matter of audio DSP coders stubbornly insisting on not using long data words on the grounds it doesn’t matter to the sound. This, when the filters go obviously wrong under some conditions for just that reason? Anyway, here’s long double biquad, because nobody else was doing it far as I know.

The second part is trickier, because if you use it you remove some functionality. Biquads make great DC blockers. But, biquads also work through the summing of many delay taps, all very close together. Some are on input, others on output. They’re a mixing of multiple copies of the signal.

That means Console applies to the biquad filter.

We already knew that, of course: I’ve long observed that you can put Console (or BussColors4/ConsoleBuss4) around a bog-standard DAW EQ and get an enhanced sound out of it. Mind you, I wasn’t controlling that EQ, but it still worked. But now, I have Console5 (not 6, but I COULD do 6 in the right context) built right into Biquad. So, it does expect to have a signal between -1 and 1 (or lower than 0dBFS in the DAW), and that means Biquad itself can’t remove huge DC offsets ten times the size of the audio content. (It can still remove smaller offsets just fine). And it runs into basically PurestConsoleChannel, does the biquad, then uses PurestConsoleBuss and goes out to an inverse/dry/wet control (which itself has multiple uses).

What’s a biquad, you ask? The Airwindows biquad uses four of the six common biquad options (I prefer to do shelves with subtractive/additive use of filtered audio). The top control has settings one through four. They go lowpass, highpass, bandpass and notch. That’s what I consider the platonic set of biquads, and it lets the filter design be simple and clear. You can set a frequency (in ‘amount of the audio range’) from ‘zero’ to ‘one’. There’ll be EQs with more specific frequencies, that’s easy, but this is proof of concept and to be used by ear, plus it will always cover DC to Nyquist at any sample rate. Zero is not really DC, because that kills the biquad: also, One is not really the Nyquist frequency (half the sample rate) for the same reason. But, they act a lot like they range that far, because the high resolution lets Biquad calculate things accurately even that far out of the normal range.

They don’t update/recalculate every sample, but the way I’ve defined the data structures means they could if you wanted them to (at a cost in higher CPU-eating). The code’s MIT licensed open source, so GPL people can just take it if they credit me, and all the projects that are using the Airwindows library are advised to get up to date and include this one. Set right, it is THE ultimate sample-instrument tone shaper to sit ‘under the hood’ and voice somebody’s musical product after the sample-playback stuff is taken care of. You’ll be seeing a lot of stuff come out that uses this code, as there are many plugins that require this type of filter to work, often ones that will benefit from the sonic improvements that are part of Biquad.

More will be revealed. Suffice to say this is a very useful building block that’ll allow for some very special plugins.

I did it because thanks to Patreon I’m still here working full-time years after I went open source. It’s really that simple: I didn’t have to stop. Nor did I have to get a ‘real job’, or make all my work proprietary or any of that. It’s not a huge living, but in fairness if I start earning a huge living I’ll only buy gear to make stuff that I can sell to people at cost, so I’m not destined for Cancun or Vegas in any event. I like what I do, so more money only means I get to do more of it. Maybe I can buy rarer gear and then make plugins of it, or a computer that could really start to make proper use of modern DAW-like things like VCV Rack (which I can’t really run that well on my older iMac… not at the scale I’d find necessary).

Also, like I said in the video, DISlike and subscribe on YouTube. I want to do an experiment to see if that hurts or actually helps. Since I can get away with it and normal youtubers can’t, please DISlike and subscribe to my videos, and I’ll see if that is really just another ‘engagement’ metric or hurts or maybe even is the secret to why so much junk thrives on youtube (maybe it’s better than likes! We’ll find out)

:)