Aliasing

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briandc
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Aliasing

Postby briandc » Mon Feb 13, 2017 8:56 pm

Hi all,
does anyone know if there is an app available that monitors for aliasing? I'd like to be able to make sure what I'm playing doesn't produce aliasing, and apart from my own ears, I'd like something a bit more precise.

brian
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bluebell
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Re: Aliasing

Postby bluebell » Tue Feb 14, 2017 11:53 am

How should these aliases occur? The audio interface's low pass input filter will not allow aliasing.

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tramp
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Re: Aliasing

Postby tramp » Tue Feb 14, 2017 7:03 pm

bluebell wrote:How should these aliases occur? The audio interface's low pass input filter will not allow aliasing.


Aliasing produced by softsynths, for example, mostly produced by hard clipped signals, cant be removed afterwards, by no low pass filter in the world, without removing parts of the signal.
You need to take care that it don't happen. (By oversampling and low pass filtering, or, by careful designed clipping logarithm.)
Aliasing in analog signals simply didn't exist.

As far I know, there is no such a plug like "Aliasing Warning". :(

ssj71
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Re: Aliasing

Postby ssj71 » Wed Feb 15, 2017 4:54 pm

I suppose if the app/plugin took the unprocessed input (e.g. raw guitar, midi notes) and the processed output (distorted guitar, synth output) it could try to guess whether any content lower than described by the input is intentional (like a octaver, or a sub osc), and/or inharmonic (which could also be caused by FM). I think it wouldn't be especially useful because you have to know what you are looking for with respect to the settings of your synth or distortion. Aliasing can also wrap around so far that it is in the same range as the intentional signal. You can sometimes get away with a little aliasing without it becoming audible... basically there's a lot of context to take into account.

For now I'd just connect a scope to the output and look for frequency content that wraps around into the lower registers (when/where you wouldn't expect).
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briandc
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Re: Aliasing

Postby briandc » Wed Feb 15, 2017 9:01 pm

Thanks, everyone. The scope idea sounds like a good option. And, re-reading a thread just now at the Audacity forum (that was written by yours-truly), I was reminded that I could record in oversampling and then down-sample and perhaps with good results, as it would seem that Audacity has anti-aliasing filters to avoid any problems when doing the down-sampling.
So I've got something to test out now, and curious to see the possible results! :)

brian
Have your PC your way: use linux!
My sound synthesis biome: http://www.linuxsynths.com


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