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Ooooh... Charts and Graphs

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BillyZeppa

Power User
Does the aliasing have any relation to why many older modelers were hard to get in the mix(too loud-steps on other instruments or not loud enough)?
Could also be the flatness of the tone, or the simplicity of modelling, producing a more stationary lifeless tone, rather the the 'evolving' distortion points of a better model.
 

philipacamaniac

Fractal Fanatic
Actually it can be argued that the sampling rate is some very high, finite value equal to the quantum time interval (in theory time is not continuous but quantized like everything else in the universe).

This hurts my brain, in the same way that it hurt my brain when Hawking explained that time didn’t exist before the Big Bang. IANATP (I am not a theoretical physicist) for sure.
 

ETOLKIEN

Experienced
Me neither, but I had some readings and my poor brain tries to scratch the surface.

There's a hypothesis that proposes that time is not continous and this could explain many unknown events in the universe.
You can consider light as a stream of discrete (indivisible) quantized packs: Photons.
In the same way, it has been theorized that time is a stream of Chronons.

When Cliff sais “Quantum time intervals” is refering to the briefest unit for measuring time, a “time particle” if you want:
https://en.wikipedia.org/wiki/Chronon

If you like the subject the gravastar concept is exciting
https://en.wikipedia.org/wiki/Gravastar

...but all this is theory!


In this case one could say that analog amps also alias, but it's beyond any measureability.

Mmmh...I would’nt say that...analog circuits don’t alias because don’t sample nothing.


Aliasing occurs when you capture a signal. The capture implies that you take a set of samples in time. When you take your pile of samples and reconstruct the signal you will see that the result will differ from the original. The whole process has introduced some artifacts (this anoying harmonics that folds back in the audible spectrum).

Note that aliasing can be reduced but can not be erased completely, is inherent to the digital capture. All of us will be happy if Cliff can reduce it to where’s below the thermal noise, never will be zero but so low that can be negligible...more than enough!

When Cliff says

Analog circuits are analogous to a digital circuit with infinite sampling rate.

Is doing an analogy, but don’t take the words literally. No sample no aliasing.
 

Sacha

Inspired
The issue of aliasing within amp modelers doesn't happen at track sample rate (e.g. input 48 kHz vs. 192 kHz), but within the amp modeling. So it would depend on whether Helix Native plugin's amp models over-samples more than the hardware Helix unit.

I'm not sure that's the case, plugins process audio at the native sample rate in the DAW (+ any applicable oversampling) as far as I am aware.
 

vangrieg

Power User
I'm not sure that's the case, plugins process audio at the native sample rate in the DAW (+ any applicable oversampling) as far as I am aware.

Actually, Helix Native downsamples everything to 48 kHz whatever your project is set to.
 

yeky83

Power User
I'm not sure that's the case, plugins process audio at the native sample rate in the DAW (+ any applicable oversampling) as far as I am aware.
Right... and we're talking about the "+ any applicable oversampling" part. The discussion is aliasing within amp-modeling.

Actually, Helix Native downsamples everything to 48 kHz whatever your project is set to.
How'd you find that out? (That was my guess since it converts the IRs it uses to 48 kHz.)
 

vangrieg

Power User
How'd you find that out? (That was my guess since it converts the IRs it uses to 48 kHz.)

It wasn’t me. If I find the source, I’ll post the info here, although it was in Russian originally.

You can sort of see what’s happening indirectly because CPU usage grows at sample rates other than 48.

EDIT: here’s the link - https://forum.guitarplayer.ru/index.php?topic=376722.msg10391222#msg10391222

Like I said, it’s in Russian (Putin’s hackers did it, as usual :)), but I’ll explain. The guy made an empty preset with no effects (first screenshot), and passed noise through the plugin at different sample rates. You can see anti-aliasing filters at work at all rates except 48 kHz, so there’s resampling going on there.
 
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yeky83

Power User
It wasn’t me. If I find the source, I’ll post the info here, although it was in Russian originally.

You can sort of see what’s happening indirectly because CPU usage grows at sample rates other than 48.

EDIT: here’s the link - https://forum.guitarplayer.ru/index.php?topic=376722.msg10391222#msg10391222

Like I said, it’s in Russian (Putin’s hackers did it, as usual :)), but I’ll explain. The guy made an empty preset with no effects (first screenshot), and passed noise through the plugin at different sample rates. You can see anti-aliasing filters at work at all rates except 48 kHz, so there’s resampling going on there.

Awesome! Russian gear heads! lol
Do you know Russian? Google Translate works well for me here :p
 

ETOLKIEN

Experienced
Awesome! Russian gear heads! lol
Do you know Russian? Google Translate works well for me here :p

I like the fact that he talks about the "Nyquist-Kotelnikov frequency", actually we have to give credit to many people for sampling theory: Harry Nyquist, Claude Shannon, Vladimir Kotelnikov and E. T. Whittaker among others.

I was reading a bit about nonuniform sampling (samples not taken equally spaced in time) as an alternative to filters to avoid aliasing, I'm sure Cliff is aware of this type of sampling and its possible drawbacks:
https://en.wikipedia.org/wiki/Nonuniform_sampling
http://www.edi.lv/media/uploads/UserFiles/dasp-web/sec-5.htm
 
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bwanagary

Administrator
Moderator
looks more like this fellow furry friend

SIMON'S CAT RULES! :)
 

yeky83

Power User
I like the fact that he talks about the "Nyquist-Kotelnikov frequency", actually we have to give credit to many people for sampling theory: Harry Nyquist, Claude Shannon, Vladimir Kotelnikov and E. T. Whittaker among others.

I was reading a bit about nonuniform sampling (samples not taken equally spaced in time) as an alternative to filters to avoid aliasing, I'm sure Cliff is aware of this type of sampling and its possible drawbacks:
https://en.wikipedia.org/wiki/Nonuniform_sampling
http://www.edi.lv/media/uploads/UserFiles/dasp-web/sec-5.htm
Interesting! Read it quick, so I dunno at all :p But...

It seems to still basically follow the Nyquist principle?
"average sampling rate (uniform or otherwise) must be twice the occupied bandwidth of the signal... if the frequency locations are unknown, then it is necessary to sample at least at twice the Nyquist criteria"

And since the Axe-Fx can filter signals as it oversamples, nonuniform sampling might not be so beneficial?
"Randomized sampling may prove to be more profitable when it is undesirable or even impossible to prefilter signals before... the signal to be processed contains components at frequencies exceeding half of the sampling rate"
 

Fractalist

New Member
Apparently Kemper has NO ALIASING as it’s not a modeler and process the signal in a very much simpler way (that’s also why they don’t need any expensive DSP, running on a 10 years old chip...)
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
Apparently Kemper has NO ALIASING as it’s not a modeler and process the signal in a very much simpler way (that’s also why they don’t need any expensive DSP, running on a 10 years old chip...)
Kemper has worse aliasing than most modern modeling products. Among the worst I've measured actually. That 10-year old chip doesn't have enough processing power to oversample adequately to suppress the aliasing.

Whether a product is a modeler or a "profiler" (which is just a modeler with gain and EQ matching) it still produces harmonics and those harmonics will alias if the oversample rate is insufficient.

The worst I ever measured was the Behringer V-Amp but I think it cost about $150 so...
 

axifist

Experienced
If the Kemper has such bad aliasing, I'm wondering, how big of an impact aliasing really has, because of its highly praised sound quality.
 
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