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Ooooh... Charts and Graphs

FractalAudio

Administrator
Fractal Audio Systems
Moderator
So, given that there are no frequencies above nyquist, why is the aliasing at all? I guess I should study up, eh?
Because those frequencies are created when the amp distorts.

It's like this. You play a high A on your guitar. That's 880 Hz. This note also has overtones at 2.64 kHz, 4.4 kHz etc. Those tones go into your amp (or amp model) and they are distorted. When you distort a signal you create harmonics of that signal. So the 4.4 kHz signal creates harmonics at 8.8 kHz, 13.2 kHz, 17.6 kHz, etc., all the way out to infinity in theory and up to tens of kHz or more in practice.

There's a harmonic at 26.4 kHz. That's above Nyquist. That harmonic "folds back" into the audible spectrum (it would fold to the image frequency of 21.3 kHz). Any harmonics above Nyquist fold into the audible spectrum.

Oversampling is how you reduce aliasing. Oversampling increases the Nyquist frequency to a multiple of the native Nyquist frequency. For example if you oversample by 8 it's the same as if you ran your A/D converter at 384 kHz so Nyquist is now at 192 kHz. This requires 8 times as much CPU time though. The more you oversample the less aliasing but the more CPU required.
 

symphx

Fractal Fanatic
Yeah words words words. But glad they are in our favor. I’ll just keep using ears. I will say I remember my boss gt10 with craaaaazy aliasing!
 

guitarmike

Experienced
Ahhhhh!!!!! You crazy genius dude!!! So, why not increase the sample rate? Wouldn't increasing to 96k or 192kprevent any aliasing at all? Does that cause other issues making it not worthwhile?
 

NeoSound

Fractal Fanatic
I’m curious to hear this. If I a/b the III and other devices is it very noticeable? (when I get one of course)
 

chris

Legend!
I’m curious to hear this. If I a/b the III and other devices is it very noticeable? (when I get one of course)
i've been working with the II and III a lot lately for testing. i know there's all this technical stuff explaining what's going on, but i don't know that stuff too well. all i know is that playing the III definitely FEELS great and sounds even "clearer" if that makes any sense.

the II does not sound or feel any worse than it ever has though; please don't start that thought. i use the AX8 weekly and it's better than anything else on my stages. but going back and forth between the 2 platforms, i definitely love what the III offers.

and we're JUST getting started...
 
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