TL;DW: Stonefire is the non-EQ EQ designed for ConsoleX.

Stonefire.zip(516k)

There’s a reason people have never turned to using Kalman filters for audio purposes.

They’re tricky little buggers, unpredictable, with a ‘filter slope’ that makes no sense at all. They’ll take the crossover point and bounce it around wildly, they’ll throw in weird gatey behaviors, they’ll turn what’s supposed to be a ‘smooth’ ‘filtered’ sound into an edgy growl and sputter. They’re meant to pull real data out of a pile of noise, not to take real audio and give you anything sensible. Nobody would want a Kalman filter for audio purposes.

Stonefire uses two different kinds of Kalman filters for audio, as crossovers. The top crossover is the same as what’s in Air3. The bottom crossover comes with a range control (even though that won’t give you a ‘frequency’) and is the same as what’s in Kalman.

And when used properly, Stonefire gives you unprecedented levels of tonal control over the texture and presentation of your sound, in a way that almost doesn’t even have to do with frequency.

There’s three bands, plus the Range control. Air, Fire, and Stone. Each can be cut back to zero, or boosted (Fire and Stone match, while Air has a lot more gain on tap but will match from 0.5 down to 0.0.) If you cut them back to zero you’ll get the weird Kalman behavior, but it’ll help you set the Range control appropriately. You can set it so Stone covers the lowest lows (never JUST those, it will always do other stuff too) or up to the high mids and lower treble.

Then, if you keep everything balanced and make smaller adjustments, the secret of the Kalman filter emerges. You have to use it as a crossover, and let it apply its incredibly strong character to texture, not frequency. It utterly fails to be a ‘filter’, but it’s an extraordinary texture-shaper, and it’s what I’m going to be building the upcoming ConsoleX system around.

Use the Air control like you would in Air3. You can cut back super-highs while seeming to not affect the brightness at all, with a strikingly natural effect. Or, boost it to bring that sparkly aura and light up the sound. It’s a custom algorithm that deals with high sample rates by just ramping up the boost: treat it with respect, but it’s there to serve your needs for glitter or lack of same.

Use the Fire control like it was an attitude knob, as much as a midrange. You can get a lot of wildness out of this one with careful settings of Range. Between Fire and Stone, only one can be louder: it’s a crossover. If you’re boosting Fire, that means you want your sound to command attention.

Use the Stone control like it’s the bedrock of your sound. If you lean entirely on it and kill all the Fire, you’ll get a monumentally heavy, sputtering, gatey foundation that zeroes in on the lowest lows, but also tries to put backbone behind anything it thinks is heavy and powerful. This includes lower midrange. Cutting it can control unwieldy bass, but adding it isn’t the same as adding a ‘bass boost’: it’ll zero in on things like kick weight and try to present them with unnatural isolation. The secret to adding weight with the Stone control is to let it not seem to be that much of a boost: you can transform the feel of a sound well before you hear ‘added bass’. You can also dial the Range up and use the same effect up into the midrange, for an intensely solid punchy character anywhere a sound seems flimsy.

God help you if you try to measure this thing with PluginDoctor or SPAN. I don’t even have any idea what will happen. It’s all made out of Kalman filters, which are not for use with audio.

Except… when they are ;)

Enjoy the new tone shaping. If it’s too ugly, use way less, see how it treats you :)

download 64 Bit Windows VSTs.zip
download Signed M1/Intel Mac AUs.dmg
download Signed M1/Intel Mac VSTs.dmg
download LinuxVSTs.zip
download LinuxARMVSTs.zip for the Pi
download Retro 32 Bit Windows VSTs.zip
download Retro PPC/32/64 Mac AUs.zip
download Retro PPC/32/64 Mac VSTs.zip
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All this is free and open source under the MIT license, brought to you by my Patreon.
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TL;DW: Kalman is not a real filter!

Kalman.zip(501k)

So… come with me, if you will, on this journey.

There’s a huge amount of audacious Airwindowsness that hinges on this little bit of code that was never meant to work for audio purposes. This isn’t just from finance or science, it’s literally from GPS satellites and their care and feeding.

Meet Kalman. To the best of my knowledge, nobody has this as an audio filter up to now. And now you do, and you’re staring at it going ‘wait, what?’, and rightly so. At first glance this ticks none of the boxes, and then it sounds awful.

What’s happening? Kalman is ‘filtering’, but really it’s trying to predict a ‘real’ position from what it sees as hopelessly noisy data. The thing is, it’s the audio input data. None of it is ‘wrong’ in any sense. In other situations I go to great lengths to preserve every detail, and here Kalman is, trying to get rid of ‘mistakes’ that aren’t even mistakes.

However, this is also how Air3 got its amazing ability to extract or suppress the air band. So what happens when you’re sweeping it from the highs right down through the midrange, into bass and beyond?

Bad things. It neither knows nor cares what a frequency is, or whether it’s producing a filter slope. Really, it’s not. It’s producing wavelike outputs like it was charting a GPS course and only roughly correlating them to audio frequencies. It won’t produce sharp breaks in its curve, but the farther you go down, the more its ‘steering’ will interfere with the audio, producing a sort of grinding, overbearing solidity, like the audio was freezing solid or turning to stone.

This is not even an audio filter, remember. I’m sure anyone who’s tried this, abandoned it, immediately, because you set it to full-wet and it immediately sounds awful.

More fools they!

This thing is best experienced not as a synth-style filter, not some sweepable musical thing, but as a crossover. You can hear either it, or on the ‘inv’ setting, its opposite. You can subtract its output from the dry signal, and then recombine them again. Works just fine in fact. And that’s where things get really interesting.

Full wet produces this unbearably heavy, petrifyingly solid, unyielding sound. Up higher it’s an exaggerated version of the Air3 roll-off. It makes everything dead, weighty, even when higher frequencies burst through in artifacts it’s like they’re the bones of the sound you started with. It’s a really strong texture.

When you subtract it, you’ve got this hot, lively, aggressive texture. It’s fiery, energetic, a little like my old plugin Cojones which identified unpredictable elements in the sound in the treble regions. This will do it at any tonal range: I’d say frequency, but the whole effect defies frequency. You can have opposite tone colors with your opposite frequency ranges: low/stone, high/fire. At the extremes, the effect is so aggressive it’s disruptive and sounds broken and wrong.

And then… just blend them more subtly, and Kalman shows what it’s really for.

When both elements are present (in this one, it’s inv/wet settings that are near the center and mostly dry, but it’d also work as Fire/Stone faders meant to stay mostly balanced) you can lean the whole texture in different directions across an amazingly wide range of basic tonality. You can fool with just the deep subs, making them monumental or leaning them out. You can darken abrasive upper mids, or mid-mids, or, heck, lower mids if you like. Above the range will be more or less Fire, below will be more or less Stone. The range, however, will never be just an isolated ‘cutoff frequency’ because the whole thing completely transforms that whole range.

If you can transform how you hear away from ‘frequency’ and hear things in terms of texture, you can apply sound changes completely unattainable by normal filtering, no matter how complex. And the neat thing is, since it’s a form of crossover, it excels at subtlety. And since the range options (shown here as simply ‘Kalman’) are so wide, you can transform texture of all sorts, not just ‘stone = heavy = weight = bass’. Heck no! You can adjust a piano to have weightier low midrange if you like, or take a drum room sound and make everything over the bass frequencies more fiery. You can take a big guitar amp, crank the weight, and then just sneak up the Kalman knob until the brutality of the lows are undeniable.

There will be more like this, as seen in the video. But Kalman is here now. You’re welcome to begin playing with it. If it fights you, don’t give up on it too easy. You might be able to do more with less. I think in many cases that inv/wet control is going to hover nearly exactly halfway. It won’t take much to get this plugin doing obvious texture shaping. The rest is up to you…

download 64 Bit Windows VSTs.zip
download Signed M1/Intel Mac AUs.dmg
download Signed M1/Intel Mac VSTs.dmg
download LinuxVSTs.zip
download LinuxARMVSTs.zip for the Pi
download Retro 32 Bit Windows VSTs.zip
download Retro PPC/32/64 Mac AUs.zip
download Retro PPC/32/64 Mac VSTs.zip
Mediafire Backup of all downloads
All this is free and open source under the MIT license, brought to you by my Patreon.
VCV Rack module