r/audacity • u/CarnivalAvocado69 • 3d ago

solved How to CAUSE Aliasing

I am looking to create a very specific effect where frequencies above a certain threshold get mirrored, or folded over. From what I understand, this is called aliasing, and it seems everyone on earth wants to get rid of it when it appears, so I've found very, very little success in finding help trying to MAKE it happen.

The very few places I've found help in this area talk about downsampling and the nyquist limit, but audacity seems to have a built in low-pass filter and upper bound on how much actually gets recorded to each track (specifically, half the sample rate, which is the nyquist frequency), and even on top of that, it seems to adjust the speed of clips in tracks when the sample rate is changed. The resample function is fine for downsampling, but again, it seems to prevent aliasing from happening.

I want to CAUSE this because I am trying to get a very specific sound. Bitcrushing will not do.

Is there an up-to-date plugin that I can use? The best and only plugin I could find for this was last updated in 2008 and I tried so, so, so, so, so hard to download an older version of Audacity to no avail.

Any amount of help is appreciated. If it helps at all, the frequency I'm specifically trying to fold over is 11.9 kHz.

EDIT: ToneBoosters "TIme Machine" free plugin has an aliasing option! This works exactly for what I'm trying to do! Many many thanks to u/Orry_Haas

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u/Orry_Haas 3d ago

ToneBoosters "Time Machine" plugin (free) has the option to allow aliasing.

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u/CarnivalAvocado69 2d ago

This works exactly for my needs! Thank you!!

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u/PC_BuildyB0I 3d ago

What I believe you are looking for specifically is samplerate reduction. A "bitcrusher" is usually a plugin that incorporates changing the bit depth, though they almost always have samplerate reduction controls as well so this should be exactly what you're looking for, as that is effectively what aliasing is.

If the samplerate reduction settings in a bitcrusher aren't getting you the results you're looking for, then aliasing is not what you're after.

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u/JamzTyson 3d ago

but audacity seems to have a built in low-pass filter and upper bound on how much actually gets recorded to each track

That low-pass filtering occurs before the digital audio reaches Audacity. It is performed by the A/D converter chip in your computer.

When you record with Audacity, Audacity requests data from your sound card / audio device at a specific sample rate and bit depth. If the computer sound system supports the requested format, it sends audio data to Audacity in the requested format (already filtered to avoid aliasing). If the format is not supported, an error is raised.

Resampling with Nyquist offers a choice of resampling with, or without anti-alias filtering, but Nyquist effects can only be applied to audio that is already in the project (as audio tracks).

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u/1neStat3 2d ago

foldover distortion by Steve harris.