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Which (free) FX to fix aliasing?

VST, AU, etc. plug-in Virtual Effects discussion

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BachRules
Banned

Postby BachRules; Thu Mar 13, 2014 3:23 am Which (free) FX to fix aliasing?

Hearing some bad high-frequency noise from EWQL Choirs, and wondering which FX to use to treat the problem?

A sample of the problem is the 2nd note in this WAV file:

https://drive.google.com/file/d/0B5ZYXb ... sp=sharing

From the zillions of good, free EQ's and filters available, any recommendations particularly suited to this task? Thank you.

Edited to add: If there is an art to this process, anything I should know? Or I just sweep until I locate the problem frequency and apply the steepest, deepest notch possible?
Last edited by BachRules on Thu Mar 13, 2014 5:10 am, edited 2 times in total.
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murnau
KVRAF
 
2695 posts since 13 Jan, 2005, from Deutschland

Postby murnau; Thu Mar 13, 2014 3:26 am Re: Which (free) FX to fix aliasing?

try out the excellent free stuff from robin schmidt @ http://www.rs-met.com/freebies.html

ps. voxengo redunoise is great but not free and 32bit still.
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BachRules
Banned

Postby BachRules; Thu Mar 13, 2014 4:15 am Re: Which (free) FX to fix aliasing?

murnau wrote:try out the excellent free stuff from robin schmidt @ http://www.rs-met.com/freebies.html

ps. voxengo redunoise is great but not free and 32bit still.


I am a voxengo fan, but I'm guessing this problem is conducive to a free solution. schmidt's products look very nice; I'll try them. Thanks.
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Sendy
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4516 posts since 20 Jul, 2010

Postby Sendy; Thu Mar 13, 2014 4:38 am Re: Which (free) FX to fix aliasing?

Thing is, aliasing doesn't happen at one frequency that you can filter out, it moves depending on the note produced, and it meshes with the musical part of the signal. I don't think I can envision a way of removing alising after the fact that isn't clumsily removing audio and muffling the sound.
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whyterabbyt
Beware the Quoth
 
21641 posts since 3 Sep, 2001, from R'lyeh Oceanic Amusement Park and Funfair

Postby whyterabbyt; Thu Mar 13, 2014 5:30 am Re: Which (free) FX to fix aliasing?

Sendy wrote:Thing is, aliasing doesn't happen at one frequency that you can filter out, it moves depending on the note produced, and it meshes with the musical part of the signal. I don't think I can envision a way of removing alising after the fact that isn't clumsily removing audio and muffling the sound.


Yup.
To laymen, software development is something akin to wizardry. Neither time, nor effort are involved. If software is missing features they want, or has bugs, it is solely because someone has been too lazy to wave their magic wand.
BachRules
Banned

Postby BachRules; Thu Mar 13, 2014 6:36 am Re: Which (free) FX to fix aliasing?

Sendy wrote:Thing is, aliasing doesn't happen at one frequency that you can filter out, it moves depending on the note produced, and it meshes with the musical part of the signal. I don't think I can envision a way of removing alising after the fact that isn't clumsily removing audio and muffling the sound.


I'm not sure it's aliasing, but it's high pitched and surely doesn't belong. I don't hear it changing frequencies, so I'm guessing I'll have some success, even if some good parts of the signal get removed in the process. Muffled would be better than high pitch giving me a headache and probably causing permanent hearing loss.
mystran
KVRAF
 
4234 posts since 11 Feb, 2006, from Helsinki, Finland

Postby mystran; Thu Mar 13, 2014 8:33 am Re: Which (free) FX to fix aliasing?

The easy way to identify typical aliasing is to do a slow pitch bend; if there are frequency components moving in the wrong direction, then you are suffering from aliasing. If the artifacts stay fixed, then it might be something else.
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BachRules
Banned

Postby BachRules; Thu Mar 13, 2014 9:51 am Re: Which (free) FX to fix aliasing?

mystran wrote:The easy way to identify typical aliasing is to do a slow pitch bend; if there are frequency components moving in the wrong direction, then you are suffering from aliasing. If the artifacts stay fixed, then it might be something else.


This is a good idea. When I use the pitch wheel, however, I get no pitch bend. I don't know this product well enough yet to know if there's another way to do pitch bend. Thanks for the advice though. I'm trying to pinpoint the location of the noise that's bugging me.
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Sendy
KVRAF
 
4516 posts since 20 Jul, 2010

Postby Sendy; Thu Mar 13, 2014 9:55 am Re: Which (free) FX to fix aliasing?

If the artifact isn't moving around when you play different pitches, it's almost certainly not aliasing. It could be some other sampled-in artifact. If it's just a ringing tone a notch filter should be able to kill it. Just slowly roll the cutoff around until it fades away. If it's an unwanted resonance from the instrument/acoustics, some gentle EQ cut in the area should help.
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mystran
KVRAF
 
4234 posts since 11 Feb, 2006, from Helsinki, Finland

Postby mystran; Thu Mar 13, 2014 10:20 am Re: Which (free) FX to fix aliasing?

Sendy wrote:If the artifact isn't moving around when you play different pitches, it's almost certainly not aliasing. It could be some other sampled-in artifact.


It could still be aliasing from interpolation in a sampler that has separate waves for each note (and the sampling rate doesn't match the host rate, so resampling is necessary), hence the suggestion to try pitch bend. But yeah, ultimately there's not much one can do beyond filtering.
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BachRules
Banned

Postby BachRules; Thu Mar 13, 2014 10:53 pm Re: Which (free) FX to fix aliasing?

Does any besides me hear the problem? Here is a new demo:

https://soundcloud.com/ammonium-nitrate ... -test-file

The file is 5 notes -- g, f, e, d, c. The "e" has the high pitch which is bugging me. The file repeats the 5-note sequence 4 times for convenience.
Last edited by BachRules on Fri Mar 14, 2014 3:14 am, edited 1 time in total.
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Tronam
KVRAF
 
1550 posts since 14 Mar, 2002, from Seattle, WA - USA

Postby Tronam; Thu Mar 13, 2014 11:07 pm Re: Which (free) FX to fix aliasing?

Depending on how severe it is iZotope RX may help. It isn't cheap, but I've managed to seamlessly repair audio that was riddled with high frequency artifacts which would've been nearly impossible to achieve using static notched EQ bands. It has one of the most intuitive spectrum visualizers I've ever seen and in most cases artifacts like that are plainly visible. They can be "cloned" out not unlike tools in Photoshop like the healing brush. Might be worth checking out the demo if you haven't already; I'm pretty sure it's fully functional for 10 days or so.
BachRules
Banned

Postby BachRules; Fri Mar 14, 2014 12:28 am Re: Which (free) FX to fix aliasing?

I pegged it with a narrow notch.

https://docs.google.com/document/d/1Aa3 ... sp=sharing

That solves my problem, but I'm still curious what the noise is; whether it really entered the microphone like that, or whether it was introduced later.

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