KVR Audio

BachRules · Post by **BachRules** » Thu Mar 13, 2014 11:23 am

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?

murnau · Post by **murnau** » Thu Mar 13, 2014 11:26 am

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.

BachRules · Post by **BachRules** » Thu Mar 13, 2014 12:15 pm

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.

Sendy · Post by **Sendy** » Thu Mar 13, 2014 12:38 pm

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.

whyterabbyt · Post by **whyterabbyt** » Thu Mar 13, 2014 1:30 pm

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.

BachRules · Post by **BachRules** » Thu Mar 13, 2014 2:36 pm

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 · Post by **mystran** » Thu Mar 13, 2014 4:33 pm

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.

BachRules · Post by **BachRules** » Thu Mar 13, 2014 5:51 pm

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.

Sendy · Post by **Sendy** » Thu Mar 13, 2014 5:55 pm

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.

mystran · Post by **mystran** » Thu Mar 13, 2014 6:20 pm

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.

BachRules · Post by **BachRules** » Fri Mar 14, 2014 6:53 am

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.

Tronam · Post by **Tronam** » Fri Mar 14, 2014 7:07 am

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 · Post by **BachRules** » Fri Mar 14, 2014 8:28 am

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.

Which (free) FX to fix aliasing?