Airwindows Ultrasonic: Mac/Windows/Linux AU/VST

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https://www.youtube.com/watch?v=7S2r-FpHvfw

TL;DW: Ultrasonic is a very clean, plain, high quality supersonic filter, for using inside digital mixes.

Ultrasonic

Now here's a handy little utility plugin… sort of the ultimate Airwindows plugin, not only does it not have an interface, it doesn't have a sound! :D

Here's why you should care… especially if you work at high sample rates.

Aliasing in digital mixes is annoying. You typically don't hear it directly, but it coarsens and flattens the mix, throwing all sorts of funny harmonics in there at random frequencies, like subtly ring modulating everything (the aliased harmonics go off on frequencies not related to the original notes, and clash). It's often very subtle, but it turns up everywhere you have nonlinearities. If you distort stuff in digital mixes, you run straight into aliasing problems. Same if you compress, or do anything nonlinear… and even if you make a mix as pristine and minimal as possible, if you're mixing in the Airwindows Console system that uses nonlinearities too.

You can run at higher sample rates and that gives you more room, you can use soft saturations (like what's in Console) and that makes the harmonics appear in order so only the highest frequencies will fold back and alias, but it's in a computer: you'll always run into the limits of juggling numbers and calling it music, and you'll experience aliasing through nearly anything you do.

But what if you just took those problem frequencies away?

Ultrasonic is very simple. It has no controls. It's a really steep lowpass filter at 20K (five poles, and it works out to 10th order Butterworth filtering). Unlike some 'audible' Airwindows filters that are supposed to sound interesting, Ultrasonic doesn't use internal Console processing: that would be a nonlinearity, and defeat the purpose. Instead, it's a super high resolution very boring and plain supersonic filter, calculating stuff at long double resolution, dithering its result to whatever floating point buss your DAW uses, and otherwise having no sound of its own.

Drop it into your (preferably 96k or 192k) digital mix and it will clean up anything nonlinear that goes after it. This includes Console! Just because Console 'decodes' doesn't mean it can't be hurt by aliasing of its nonlinearities: it just distorts so gently that it's not automatically worse, but any aliasing that turns up in ConsoleChannel doesn't get taken away by ConsoleBuss. Digital only gets worse, not better, and the trick is to make it get worse as slowly as possible while you work with it.

When you use Ultrasonic, for instance on every channel in a Console mix, you trade a degree of rawness and immediacy for an ease and smoothness that is immediately apparent if your stuff is running into nonlinearities anywhere. In many ways it makes the digital mix sound more analog. The tradeoff is, it's still five poles of biquad filtering, and it will make stuff sound a bit slick, a bit more 'processed'. You can kinda hear that you're doing the extra processing, but the texture change is really appealing: stuff sits back (less super-treble will always sound more like the audio 'sits back' and is more polite) and bright shiny stuff sounds purer and sweeter. This is all the more true if you're processing heavily.

It's very easy to use: just put the plugin before anything that might alias. By itself it should have no sound (though if you have true 96k or 192k audio, it of course is obliterating your real supersonic content). There are no controls and nothing to do, it isn't itself nonlinear so it shouldn't interact with anything, you don't have to gain stage it or pay any attention to it at all. Very plain, simple, hopefully pretty low-CPU for all that it's five poles of filtering at stinkin-high calculation accuracy.

Put it on everything that you want to smooth out and un-digitalize. Sometimes there's nothing quite like beating the problem into the ground with a sledgehammer. For frequencies over 20K and the aliasing that loves them, this is that sledgehammer. (It is also biquad filtering, so it runs with zero latency and you can track through it)

All this is supported by Patreon. You can add a dollar to your pledge for each thousand instances of Ultrasonic you use, if you like. (careful, you might find that adding up quick!) :D

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That's awfully nice of you, thanks :]

I've been sort of wishing for a really really simple, clean cut like this--especially for when I'm compressing percussion.

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Can it be effectively used on 44.1, 48 and 88.2 or 96/192 is necessary?

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HcDoom wrote: Mon Nov 23, 2020 9:36 pm Can it be effectively used on 44.1, 48 and 88.2 or 96/192 is necessary?
Using it at 44.1 is far from effective :) it will indeed apply the same steep filter at 20K, but anything you put after it is gonna alias pretty much just as bad as if you didn't use it.

It's a lot more effective at 88.2k and up, whichever you choose to use. it'll always be the same 20K steep filter regardless, so once you have some 'room' above 20K to give you some space from aliasing, it's up to you how much room you want. Higher sample rate will resist aliasing more. It's much like oversampling everything, but without the extra SRCs inside the processing chain: instead, you're just blocking ultrasonic frequencies and going from there, and your output will be legitimately 96k or 192k, but representing sub-20K frequencies with less aliasing.

I do a MTM Chord Organ firmware to similar effect. That can produce square and saw waves, etc. and I set the sampling rate to nearly 300K. It's not to play ultrahigh notes, it's so that the midrange notes I use will be more free of aliasing and sound better :)

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jinxtigr wrote: Mon Nov 23, 2020 11:58 pm
HcDoom wrote: Mon Nov 23, 2020 9:36 pm Can it be effectively used on 44.1, 48 and 88.2 or 96/192 is necessary?
Using it at 44.1 is far from effective :) it will indeed apply the same steep filter at 20K, but anything you put after it is gonna alias pretty much just as bad as if you didn't use it.
What if it's the last plugin on the Master ? You can actually see this plugin working in SPAN.
None are so hopelessly enslaved as those who falsely believe they are free. Johann Wolfgang von Goethe

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If it's the last plugin on the master bus then all the aliasing will have happened already in all the previous plugins

Aliasing and its even uglier cousin, intermodulation distortion, aren't caused by high frequencies, even high frequencies near the Nyquist frequency—even by frequencies EXACTLY AT the Nyquist frequency.

Aliasing is caused by a non-linear effect (saturation, compression) on ANY frequency if—at any point—the effect generates frequencies and harmonics past the Nyquist frequency, at which point they will reflect down as inharmonic noise in the audible frequency ranges.

Intermodulation distortion is a non-harmonic distortion that forms between any two frequencies when operated on by any non-linear effect. The higher the bandwidth, the more frequencies there are, the more chance for intermodulation distortion to form.

It is, perhaps surprisingly, a risk in both analogue and digital systems, but analogue systems have a natural roll-off that massages ultrasonic frequencies away. Digital systems retain information up to the Nyquist frequency, which allows for a full spectrum of problems to generate.

The way to avoid aliasing is to increase the sample rate a ridiculous amount but, BUT, this allows for more frequencies in the signal, which—even though they sit way outside the range of human hearing—will generate intermodulation distortion down through into the audible spectrum, resulting in a slow, quiet, yet constant build-up of junk sounds, the more effects you apply.

The point of using this is not that adding a steep low-pass to the end of your mastering chain will suddenly make it sound better. Neither will adding it between every single plugin make it sound better.

The point at which to add this is "any time you're going to put a signal through a complicated non-linear effect, and that signal has a LOT of information up in the ultra-sonic range." Pans, gain adjustments, and send effects like delays and reverbs are practically risk-free, and you don't need this plugin. Amps/saturators are riskier. Compressors and limiters are the worst for building up audible "garbage noise" out of ultrasonic frequencies.

Essentially: if you're about to do something crazy and dynamic to a signal, and there's info in that signal which the human ear cannot hear, use this plugin. Putting it after every single plugin isn't necessary, and putting it at the very, very end of a long chain of plugins is too late to stop the problem.
Last edited by sleepcircle on Tue Nov 24, 2020 2:31 am, edited 3 times in total.

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But the plugin is supposed to fix that no ? Otherwise what's the point ?
jinxtigr wrote: Mon Nov 23, 2020 11:58 pm but anything you put after it is gonna alias pretty much just as bad as if you didn't use it.
If there's nothing after it....
sleepcircle wrote: Tue Nov 24, 2020 1:09 am there's info in that signal which the human ear cannot hear, use this plugin.
I just read your rather lengthy edit. Oh I get it now. This plugin is pointless. Got it :tu:
None are so hopelessly enslaved as those who falsely believe they are free. Johann Wolfgang von Goethe

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absolutely. you should definitely never use it.

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Watch the video again. :wink:
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None are so hopelessly enslaved as those who falsely believe they are free. Johann Wolfgang von Goethe

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It if is a placebo, why don't you show proof that it is?

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don't argue with him. i'm sure he has a gearslutz.com account; let him argue with a couple dozen engineers and mathematicians instead.

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I was trying TDRs Ultrasonic w 44.1 and couldn't hear much of a difference.

Lately I tried w 88.2 and the difference was - though subtle - immediately apparent (tried w TDR Ultrasonic, AW Ultrasonic, IIEQ band-passed @ 20Hz/20kHz&72dBoct and Melda's BandPass band-passed @ 20Hz/20kHz&72dBoct).

Chris, I think the name is recognizable now (for 6 years) with FabianS/VladG's work. maybe change it to Passonic or Passover ?
(hey ! that's a great name for a plug that's released in ..umm... PASSOVER :D )

No disrespect, just sayin'...

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This plugin is not supposed to be used at 44.1/48k, but only higher samplerates, hence the name "ultrasonic".

Fabien from TDR made a compelling case on why ultrasonic filtering is important on high sample rates when they released their tool for that (which, sadly, remained in beta stage until this day, so Airwindows version is more than welcome)
https://www.gearslutz.com/board/masteri ... ssing.html

The thread is worth a good read.

I for one noticed enough of a difference when I started inserting it at various points in my 88.2k chain to justify its continual use.

As for Teksonik, I wanted to give him thumbs down for his spam posts, but then I realized he's already on my ignore list when I logged back in.

Thanks Chris for this useful tool!

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The use of at least TDR's ultrasonic filter is to band limit your signal before you pass it over to the next process. You don't need to process anything that you don't hear after all, and all the extra bandwidth can do is cause trouble, which can end up back in the audible range.

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