Trash 2: strange DC Offset

VST, AU, etc. plug-in Virtual Effects discussion
Derozer
KVRer
17 posts since 18 Nov, 2017

Post Mon Jan 20, 2020 2:44 am

Hi people,

I'm using the awesome Trash 2 plugin to get some fancy distortion fxs.
I've a problem with a preset I'm working on.

Here's the screenshot:

Image

As you can see, its "bipolar", with the center point 0/0. But if I disable DC Offset, I have a constant DC signal coming out from the plugin.

I'd like to understand why this, learning waveshaping. at 0.0 it should be 0.0. Why that offset?

Thanks

User avatar
Tj Shredder
KVRAF
3976 posts since 6 Jan, 2017 from Outer Space

Re: Trash 2: strange DC Offset

Post Mon Jan 20, 2020 6:36 am

Its not point symmetric around 0/0. So if your input signal has no dc, the output will get one. As in your example the negative high values will go back to zero and thus you will weight the negative values less than the positive ones...
Without a dc blocker you’ll never find the good spot for you center, as it also changes with the input level. In your example on maybe -8 dB you will instead get a negative dc...
Feed a sine wave and play with the input level...

Derozer
KVRer
17 posts since 18 Nov, 2017

Re: Trash 2: strange DC Offset

Post Mon Jan 20, 2020 7:23 am

Tj Shredder wrote:
Mon Jan 20, 2020 6:36 am
So if your input signal has no dc, the output will get one.
Thanks for the fast reply dude!

Not sure I got the point though :)
NO DC input = 0.0 as input value.
Thus, having x=0.0 means y=0.0 in the graph above:

Image

That's why I don't get a +DC offset value...

meloco_go
KVRian
697 posts since 21 Sep, 2008

Re: Trash 2: strange DC Offset

Post Mon Jan 20, 2020 1:12 pm

Yeah, this should not be happening. Why it happens may range from 0 signal being not truly 0 in your DAW (maybe the dither signal is only +1 bit) or some glitch with the math on the plugin.

Derozer
KVRer
17 posts since 18 Nov, 2017

Re: Trash 2: strange DC Offset

Post Mon Jan 20, 2020 11:54 pm

meloco_go wrote:
Mon Jan 20, 2020 1:12 pm
Yeah, this should not be happening. Why it happens may range from 0 signal being not truly 0 in your DAW (maybe the dither signal is only +1 bit) or some glitch with the math on the plugin.
DAW input is 0.0 (i've analysed the samples).
Even if it was 1e-6, the added DC offset is very huge (somethings like -4DB).

Probably a Trash 2 bug. Where can I report it? Can't see any official iZotope forum...

JerGoertz
KVRAF
2723 posts since 20 Feb, 2004

Re: Trash 2: strange DC Offset

Post Mon Jan 20, 2020 11:59 pm

I've experienced something like this as well, using Trash 1 or 2. So it's not just you.
A well-behaved signature.

User avatar
DJ Warmonger
KVRAF
3689 posts since 7 Jun, 2012 from Warsaw

Re: Trash 2: strange DC Offset

Post Tue Jan 21, 2020 12:20 am

Tj Shredder already gave correct and detailed explanation of this one, so learn from smarter ones instead of weaving your own nonsense...

DC means the mean value of signal is not 0. If you feed a symmetric signal through asymmetric effect, the resulting signal will also be asymmetric and thus likely have mean value different than 0. This is what every non-linear effect does to a signal. it's not a bug, it's simple maths.
http://djwarmonger.wordpress.com/
Tricky-Loops wrote: (...)someone like Armin van Buuren who claims to make a track in half an hour and all his songs sound somewhat boring(...)

Derozer
KVRer
17 posts since 18 Nov, 2017

Re: Trash 2: strange DC Offset

Post Tue Jan 21, 2020 1:02 am

DJ Warmonger wrote:
Tue Jan 21, 2020 12:20 am
DC means the mean value of signal is not 0. If you feed a symmetric signal through asymmetric effect, the resulting signal will also be asymmetric and thus likely have mean value different than 0. This is what every non-linear effect does to a signal. it's not a bug, it's simple maths.
But... did you read the post? I don't feed any signal to it (I'm talking about this, not processing a signal). Thus "all" 0 value samples.

What's the "mean" of a all 0 data, my hero?

User avatar
DJ Warmonger
KVRAF
3689 posts since 7 Jun, 2012 from Warsaw

Re: Trash 2: strange DC Offset

Post Tue Jan 21, 2020 1:14 am

How about "drive" control? Depending on algorithm, it might introduce some bias.
http://djwarmonger.wordpress.com/
Tricky-Loops wrote: (...)someone like Armin van Buuren who claims to make a track in half an hour and all his songs sound somewhat boring(...)

Derozer
KVRer
17 posts since 18 Nov, 2017

Re: Trash 2: strange DC Offset

Post Tue Jan 21, 2020 1:23 am

DJ Warmonger wrote:
Tue Jan 21, 2020 1:14 am
How about "drive" control? Depending on algorithm, it might introduce some bias.
Tried all settings in the right panel.
Drive/Pre 0/100... changes nothing.

Of course Mix to 0 remove the DC, but because it won't mix the processing :)

meloco_go
KVRian
697 posts since 21 Sep, 2008

Re: Trash 2: strange DC Offset

Post Tue Jan 21, 2020 11:18 am

Derozer wrote:
Mon Jan 20, 2020 11:54 pm
Probably a Trash 2 bug. Where can I report it? Can't see any official iZotope forum...
There should be customer support form on the Izotope's website.

Derozer
KVRer
17 posts since 18 Nov, 2017

Re: Trash 2: strange DC Offset

Post Thu Jan 23, 2020 11:42 pm

Written ;) Let see what's they said! Thanks dudes

Derozer
KVRer
17 posts since 18 Nov, 2017

Re: Trash 2: strange DC Offset

Post Tue Feb 18, 2020 4:48 am

Here's the reply from the support:

"This is a normal behavior of Trash 2.
When enabling BiPolar, on an asymmetrical waveform, you will get 'noises' from it, because there is some type of phasing that is happening when the BiPolar feature is engaged"

Not really sure about this answer. Phasing on zero-input signal? Uhm...

TIMT
KVRian
675 posts since 8 Mar, 2009

Re: Trash 2: strange DC Offset

Post Tue Feb 18, 2020 5:30 am

I got a similar answer when i asked about this years ago and another similar bollocks answer about why when you move the centre axis from zero even the tiniest amount you get a rush of noise when the sound ends(check the crispy and capacity algorithms for a demonstration of it)they said that is how all waveshapers behave if you was to do the same thing(also bollocks)don't hold your breath that they will do anything about either of these issues :D
I

onerob
KVRist
379 posts since 28 Oct, 2014

Re: Trash 2: strange DC Offset

Post Wed Feb 19, 2020 8:12 am

There's a similar feature in Melda's MWaveShaper and you get exactly the same behaviour. It's just the way these things work. You can place a high pass filter afterwards to mitigate the effect somewhat.

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