Hardware Aliasing (Elektro Harmonix Platform)

[Habdulabaluba]

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Hey there!

I'm trying to learn more about sound and been watching a lot of videos about aliasing in digital processing. After that, I had this idea that analog processing wouldn't add aliasing (because of filters on the ADC) so I decided to buy a piece of hardware that would give me some saturation, but to my surprise it also aliased when I did some tests (videos down below!)

My test is setup like this: sine generated on Ableton Live, going out the Focusrite Scarlett (interface) to the Elektro Harmonix Platform (compression pedal with drive control), back to the interface and to the computer.

Drive Off
https://imgur.com/a/IeLfV7p (https://imgur.com/a/IeLfV7p)

Drive On
https://imgur.com/a/WoJq2wJ (https://imgur.com/a/WoJq2wJ)

I should add that I'm not clipping the interface in case that could change the results!

I was hoping someone with more knowledge than me could help figuring out:
- Why is aliasing happening in this context (and maybe some important things to read about this topic)
- How I can solve it (if possible)

Thank you in advance!! Much love!

[Viktor [TUC]]

That might be because the Platform Compressor is a digital pedal (DSP), not an analogue one.

I should add, of course being digital doesn't mean that it HAS to produce heavy aliasing. There are ways to diminish that, obviously, to the point where you can't hear it anymore. EHX could have perhaps done a bit more to prevent/reduce it, based solely on your GIFs. Not sure, haven't heard the pedal yet.

[pixel85]

Elektro Harmonix Platform is a digital compressor. It has ADC - DSP - DAC.
Once I was planning to buy it, but after long research (reading any written piece about it all over the internet), I concluded that it has max. 44.1kHz sample rate (at best) and no oversampling. This explains why you see aliasing.

More than that, in one place, someone said that it has a range of only up to 16kHz. I wonder if you could check with, e.g. white noise, to see if it goes beyond 16kHz. Your gifs are quite small, and I'm not 100% sure if sine wave cuts there.
If it really goes only to 16kHz, then it's possible that it doesn't even operate at 44.1kHz but only at 32kHz, which wouldn't make any sense.

I doubt that you can solve it. If it aliases then it aliases. Especially when it does even before you drive it higher. You would need oversampling, but then you would have to rework DSP in this pedal

[Habdulabaluba]

That might be because the Platform Compressor is a digital pedal (DSP), not an analogue one.

I should add, of course being digital doesn't mean that it HAS to produce heavy aliasing. There are ways to diminish that, obviously, to the point where you can't hear it anymore. EHX could have perhaps done a bit more to prevent/reduce it, based solely on your GIFs. Not sure, haven't heard the pedal yet.

Gotcha! I guess I should've researched a bit more to know it was a digital pedal, my brain just thought it would be analog because it was in a little box
Thank you!

[Habdulabaluba]

Elektro Harmonix Platform is a digital compressor. It has ADC - DSP - DAC.
Once I was planning to buy it, but after long research (reading any written piece about it all over the internet), I concluded that it has max. 44.1kHz sample rate (at best) and no oversampling. This explains why you see aliasing.

More than that, in one place, someone said that it has a range of only up to 16kHz. I wonder if you could check with, e.g. white noise, to see if it goes beyond 16kHz. Your gifs are quite small, and I'm not 100% sure if sine wave cuts there.
If it really goes only to 16kHz, then it's possible that it doesn't even operate at 44.1kHz but only at 32kHz, which wouldn't make any sense.

I doubt that you can solve it. If it aliases then it aliases. Especially when it does even before you drive it higher. You would need oversampling, but then you would have to rework DSP in this pedal

Sooo, I ran some white noise through it and guess what happened

Captura de ecrã 2022-04-22, às 17.24.22.png

I guess it is running at an even smaller sample rate then?

Also, is there an easy way to know if an equipment is digital or analog, or do I just have to research a lot to know how it works inside? Thank you so much for the help!

[pixel85]

Elektro Harmonix Platform is a digital compressor. It has ADC - DSP - DAC.
Once I was planning to buy it, but after long research (reading any written piece about it all over the internet), I concluded that it has max. 44.1kHz sample rate (at best) and no oversampling. This explains why you see aliasing.

More than that, in one place, someone said that it has a range of only up to 16kHz. I wonder if you could check with, e.g. white noise, to see if it goes beyond 16kHz. Your gifs are quite small, and I'm not 100% sure if sine wave cuts there.
If it really goes only to 16kHz, then it's possible that it doesn't even operate at 44.1kHz but only at 32kHz, which wouldn't make any sense.

I doubt that you can solve it. If it aliases then it aliases. Especially when it does even before you drive it higher. You would need oversampling, but then you would have to rework DSP in this pedal

Sooo, I ran some white noise through it and guess what happened


I guess it is running at an even smaller sample rate then?

Also, is there an easy way to know if an equipment is digital or analog, or do I just have to research a lot to know how it works inside? Thank you so much for the help!

LOL! Smaller sample rate would be my first guess. But who knows, maybe it is supposed to emulate 'vintage digital'? Or there's another reason like brickwall filter. Maybe someone who has this pedal and check it in and out, could know better.

Good old research is the best way to find out if pedal/effect is analog or digital but usually it's written in description and in manual. Normally in manual you can find info about sample rate and bit depth when processor is digital.

[Viktor [TUC]]

Pixel85 already mentioned it.
I'd first look into the product's manual. Being "analog" is usually something they mention right away and in bold letters. If there's no mention of analog or digital, then check if there's a forum that discusses the product.
You'll quickly find this link:
https://www.ehx.com/topic/is-the-platfo ... ed-analog/
With a clear reply too, so they're not shy about it.

[lfm]

One trick I think holds - if not single 9V battery option to run it, it usually is digital.
The digital draws more current as I found anyway.
And if on battery 6 x AA battery or similar might be digital also.

And if shipped with adapter, digital also, unless tube something.

[BertKoor]

Drive On
https://imgur.com/a/WoJq2wJ

I often read people complaining about aliasing without providing solid proof. To my surprise you have done the only right test to diagnose it as aliasing: sweep the frequency up, results in frequencies going down.

Alas not much can be done about it I'm afraid.

[vurt]

what are you using it for specifically?
full mix? or drum bus? whatever?

i use it on guitar, first in a chain of fx, and have never noticed any issues in practice.
ive never tried it on other sound sources so can't really comment on how problematic it may be?

[foosnark]

One trick I think holds - if not single 9V battery option to run it, it usually is digital.
The digital draws more current as I found anyway.
And if on battery 6 x AA battery or similar might be digital also.

And if shipped with adapter, digital also, unless tube something.

A lot of people like to say digital stuff needs more current but in practice, some analog gear has a pretty heavy draw. It's going to vary a lot with the design.

Certainly I've had all-analog gear that came with a wall wart or a laptop-looking PSU.

[vurt]

yep, plenty of analog came with power adapter.

and some digital that didn't.

[lfm]

My goodness, my scientific study on my own floorboard does not hold up.

What is this world coming to....

[zerocrossing]

That might be because the Platform Compressor is a digital pedal (DSP), not an analogue one.

I should add, of course being digital doesn't mean that it HAS to produce heavy aliasing. There are ways to diminish that, obviously, to the point where you can't hear it anymore. EHX could have perhaps done a bit more to prevent/reduce it, based solely on your GIFs. Not sure, haven't heard the pedal yet.

Gotcha! I guess I should've researched a bit more to know it was a digital pedal, my brain just thought it would be analog because it was in a little box
Thank you!

I did the same thing when I bought a Roland Torcido, which is also a digital distortion box. I loved the sound demos, and the CV in was perfect for my needs, so I just got it and later found it was digital. I’m not disappointed. It actually doesn’t seem to alias at all and sounds great.

Digital distortion can be great, if done right. It’s just often not done right.