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Amp Sim plugin and oversampling

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Amp Sim plugin and oversampling

Postby Leftyjay » Tue Jun 11, 2019 1:56 pm

Hi !
New to this forum, new to guitar recording...Hope I ask the question in the right section.

I've been playing around with amp sim since I changed my computer. I was having fun, actually bought the Mercuriall Reaxis based on reviews and whatnot. I really thought that it sounded great, better than my aging Avid Eleven Rack (or 11R) (although the addition of an external IR loader extented its life quite a bit).

With that being said, I wasn't sure what was the purpose of the oversampling in plugin and started to investiguate and closely listen through my DT880 headphones. Then it struck me.

You can clearly hear what I think we call antialiasing when the oversampling is disabled. That artifact goes slowly away and his barely noticable when oversampling x4 and above.

I attached audio samples below (first one with x1 oversampling and the other x8). Warning : not cool to listen to at all :).

It is worth noting that I don't hear that with the 11R.

Now here's my questions :

* If the plugin doesn't have oversampling directly in it, is it possible to oversample outside the plugin?

* If the answer is "no", is there a way to filter out that anoying noise?

I really want to look into other plugins, but if that means that I will hear all the time that crappy digital sound, I'll pass.

Thanks !


CLIPS :
Note : You might want to use good quality headphones or monitor to clearly hear the noise.

https://www.dropbox.com/s/34x0k5zwtnban ... 9.wav?dl=0

https://www.dropbox.com/s/4ewsls0zms481 ... 9.wav?dl=0
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Re: Amp Sim plugin and oversampling

Postby Hugh Robjohns » Tue Jun 11, 2019 2:42 pm

Leftyjay wrote:I wasn't sure what was the purpose of the oversampling in plugin and started to investiguate and closely listen through my DT880 headphones. Then it struck me. You can clearly hear what I think we call antialiasing when the oversampling is disabled. That artifact goes slowly away and his barely noticable when oversampling x4 and above.

The effect is aliasing. Anti-aliasing is the process (steep low-pass filtering, in fact) of preventing aliasing by restricting the signal spectrum to less than half the sample rate before processing.

The problem in the context of amp sims is that the aim of the sim is to introduce musically-relevant distortions, and distortion generally involves lots of strong harmonics extending far above the fundamental musical frequencies. If these generated harmonics end up being above half the sample rate, they get 'reflected' back into the audible part of the spectrum. In which case, these created signal components no longer relate to the musical fundamentals, but instead have a mathematical relationship with the sample rate. Consequently they are 'unmusical' and our ears/brain can spot them even at incredibly low levels because they sound so unnatural! ...as you have observed.

By operating the amp sim algorithms at a much higher internal sample rate -- the oversampling process -- the generated harmonics are kept below half the sample rate, and so aliasing is much less of a concern.

* If the plugin doesn't have oversampling directly in it, is it possible to oversample outside the plugin?

Yes, in theory. You would need to use a sample rate converter to raise the sample rate to 4x (or more) the project sample rate, then apply the amp sim, and then use another sample rate converter to bring the rate back down to the project rate again. However, I doubt that would be very practical within most DAWs.

* If the answer is "no", is there a way to filter out that anoying noise?

Nope. Once those alias tones are embedded within the audible part of the audio they can't (easily) be removed.

I really want to look into other plugins, but if that means that I will hear all the time that crappy digital sound, I'll pass.

The plugin ~should~ apply the proper anti-alias and reconstruction filtering itself as a part of the algorithmic process, but it seems that many do not, sadly. There's another thread discussing this same effect here: https://www.soundonsound.com/forum/viewtopic.php?f=15&t=66584
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Re: Amp Sim plugin and oversampling

Postby Leftyjay » Tue Jun 11, 2019 3:19 pm

Thanks Hugh!

For the aliasing vs antialiasing, i noticed after posting it. I searched so much for antialising lately :)

Your reply is textbook what i was looking for. Ill read carefully before buying other amp sims then.
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Re: Amp Sim plugin and oversampling

Postby Martin Walker » Tue Jun 11, 2019 4:29 pm

Hi Leftyjay, and welcome to the SOS Forums! 8-)

I've recently been exploring the amount of aliasing on various plug-ins (and have indeed abandoned a few of them having seen how much of this distortion they suffer from at 44.1kHz sample rate)

I've also been exploring various oversampling options and have discovered DDMF Metaplugin64, which is a very comprehensive 'plugin that loads other plugins. As simple as that. Build your own effect networks with this plugin wrapper using any VST/VST3 (and AU, if you’re on Mac) effect you already have on your harddisk."

https://ddmf.eu/metaplugin-chainer-vst- ... x-wrapper/

It's overkill for our application, however it does feature very effective x2/x4 oversampling options that apply to the plugins it's hosting, and this does help get rid of aliasing effects at the expense of higher CPU and a small extra latency. You can even change the oversampling 'in situ' while you're listening to audio passing through, which is a great way of hearing whether or not you can actually hear the aliasing.

Could be worth a try anyway!


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Re: Amp Sim plugin and oversampling

Postby Leftyjay » Tue Jun 11, 2019 4:34 pm

Martin Walker wrote:Hi Leftyjay, and welcome to the SOS Forums! 8-)

I've recently been exploring the amount of aliasing on various plug-ins (and have indeed abandoned a few of them having seen how much of this distortion they suffer from at 44.1kHz sample rate)

I've also been exploring various oversampling options and have discovered DDMF Metaplugin64, which is a very comprehensive 'plugin that loads other plugins. As simple as that. Build your own effect networks with this plugin wrapper using any VST/VST3 (and AU, if you’re on Mac) effect you already have on your harddisk."

https://ddmf.eu/metaplugin-chainer-vst- ... x-wrapper/

It's overkill for our application, however it does feature very effective x2/x4 oversampling options that apply to the plugins it's hosting, and this does help get rid of aliasing effects at the expense of higher CPU and a small extra latency. You can even change the oversampling 'in situ' while you're listening to audio passing through, which is a great way of hearing whether or not you can actually hear the aliasing.

Could be worth a try anyway!


Martin

I will DEFINITLY look into that !
Thanks
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Re: Amp Sim plugin and oversampling

Postby Dr Huge Longjohns » Tue Jun 11, 2019 5:29 pm

https://ddmf.eu/metaplugin-chainer-vst- ... x-wrapper/

It's overkill for our application, however it does feature very effective x2/x4 oversampling options that apply to the plugins it's hosting, and this does help get rid of aliasing effects at the expense of higher CPU and a small extra latency. You can even change the oversampling 'in situ' while you're listening to audio passing through, which is a great way of hearing whether or not you can actually hear the aliasing.

Could be worth a try anyway!

Only £34 too. Talk us through how you use it, Martin, please! Mac/Logic user here.
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Re: Amp Sim plugin and oversampling

Postby James Perrett » Tue Jun 11, 2019 8:21 pm

For users of DAWs with automatic sample rate conversion (like Reaper) you could simply set the session sample rate to be the highest that your audio interface can handle. Your 44.1 or 48kHz files will automatically be upsampled to the session sample rate before processing. Most interfaces should handle 96kHz sample rates these days which will gain you some improvement.
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Re: Amp Sim plugin and oversampling

Postby Martin Walker » Fri Jun 14, 2019 8:24 pm

Dr Huge Longjohns wrote:
https://ddmf.eu/metaplugin-chainer-vst- ... x-wrapper/

It's overkill for our application, however it does feature very effective x2/x4 oversampling options that apply to the plugins it's hosting, and this does help get rid of aliasing effects at the expense of higher CPU and a small extra latency. You can even change the oversampling 'in situ' while you're listening to audio passing through, which is a great way of hearing whether or not you can actually hear the aliasing.

Could be worth a try anyway!

Only £34 too. Talk us through how you use it, Martin, please! Mac/Logic user here.

Ah, very early days yet - I only downloaded the demo version a couple of days ago to try it out, largely so I could test two series-connected plug-ins in DDMF's most excellent PluginDoctor utility (which I do own).

It was only when browsing through the various features on offer within Metaplugin that I noticed the x2/x4 oversampling option, so I tried it out on a couple of plug-ins that I own that have visible aliasing distortion, just to see how much these two options reduced it.

It certainly made a significant difference, although having tried out oversampling options on other plug-ins (particularly clippers), my experiments suggest that x4/x8 are even more effective at removing aliasing without ramping up the CPU overheads too much (my PC ground to a halt when I attempted the artificial perfection of x128 oversampling ;) )


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