How to detect cramping and/or aliasing of an eq?

VST, AU, etc. plug-in Virtual Effects discussion
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resistent
KVRian
518 posts since 14 Apr, 2008 from Berlin

Post Wed Mar 25, 2020 3:45 am

What are the options to detect cramping and/or aliasing of an eq without an dedicated analyzer tool?
Is it fine to run a 1khz sine into an eq and take a look at SPAN? Can I detect with this setup aliasing? Hows about cramping filters how to detect those? In fact I want to investigate to eqs which I think run into cramping/aliasing (test by ear :-) ). But maybe I fool myself. The eqs in question are EQ560 by RedRockSound and PTEq-X by IgniteAmps.

Thanks for any help.

heavymetalmixer
KVRian
578 posts since 8 Jan, 2017

Re: How to detect cramping and/or aliasing of an eq?

Post Wed Mar 25, 2020 6:33 am

Run the plugin inside Plugindoctor: https://ddmf.eu/plugindoctor/
You can use it in demo permanently if you want to.
1) For cramping EQs, the main window is what you want: Make a boost or cut on the high-end and move it close to 20 KHz, You will notice that the curve will start to become narrower ONLY AT ITS RIGHT SIDE.

2) For aliasing it varies. For the most part you need to go to the "HarmonicAnalysis" tab: Start driving the plugin (mostly at the high-end on EQs), and if there's aliasing you should notice some harmonics literally bouncing back down to lower and lower frequencies. You know those are aliasing because the lower the frequency of the harmonic, the lower its volume too.

You can see some plugins having anti-aliasing because in the main tab you can see a steep LPF around 20 KHz. Now, you need to know that even the best anti-aliasing methods aren't perfect, they can be good and even reduce a lot of aliasing, but they will never completely obliterate it.
Last edited by heavymetalmixer on Wed Mar 25, 2020 11:06 am, edited 1 time in total.

User avatar
krabbencutter
KVRian
574 posts since 12 Jul, 2013

Re: How to detect cramping and/or aliasing of an eq?

Post Wed Mar 25, 2020 9:44 am

Keep in mind there's a big difference between 'cramping' and 'proper anti-aliasing'.
If your EQ graph cuts off sharply below nyquist, like in the attached screenshot, everything's fine.
Only if it starts to asymetrically warp way beyond nyquist it's actually poorly designed
You can read more on that here
https://vladgsound.wordpress.com/2015/0 ... #more-1308
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Last edited by krabbencutter on Wed Mar 25, 2020 9:51 am, edited 1 time in total.
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Burillo
KVRAF
3871 posts since 15 Nov, 2006 from Hell

Re: How to detect cramping and/or aliasing of an eq?

Post Wed Mar 25, 2020 9:45 am

krabbencutter wrote:
Wed Mar 25, 2020 9:44 am
Keep in mind there's a big difference between 'cramping' and 'proper anti-aliasing'.
If your EQ graph cuts off sharply below nyquist, like in the attached screenshot, everything's fine.
Only if it starts to asymetrically warp way beyond nyquist it's actually poorly designed
https://vladgsound.wordpress.com/tag/cramping/
just to be clear: some developers use less steep antialiasing filters, so what looks like cramping may actually be just antialiasing with a non-brickwall slope.
From Russia with love
Our online jams (if you speak Russian - you're welcome to join!)

MogwaiBoy
KVRAF
3138 posts since 26 Nov, 2015 from Way Downunder

Re: How to detect cramping and/or aliasing of an eq?

Post Wed Mar 25, 2020 11:36 pm

Yeah, it's about how the shape of the bell curve squashes (cramps) up against Nyquist as you raise it's frequency. Short sharp cut-offs above 20khz are indicative of other things, not cramping.

Recommend Plugindoctor!

User avatar
resistent
KVRian
518 posts since 14 Apr, 2008 from Berlin

Re: How to detect cramping and/or aliasing of an eq?

Post Thu Mar 26, 2020 4:57 am

Thanks folks.

I tried Plugindoctor and tested EQ560 by RedRockSound and PTEq-X by IgniteAmps as well as Molot by vladg/sound.

EQ560 by RedRockSound show whether aliasing nor cramping; there is also no saturation going on. So this eq is only nice because it adapt the API560 freqband and q.

With PTEq-X and Molot I'm not sure what happens.

(1): PTEq-X with tube emulation (not sure if just saturartion/distortion). Without tube emu there is no aliasing
(2): Molot with 8x oversampling
(3): Molot without oversampling
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vitocorleone123
KVRist
451 posts since 30 Jun, 2014 from Pacific NW

Re: How to detect cramping and/or aliasing of an eq?

Post Thu Mar 26, 2020 7:11 am

So.... those aren't the Linear charts, those are the Harmonics. Intentional?

User avatar
resistent
KVRian
518 posts since 14 Apr, 2008 from Berlin

Re: How to detect cramping and/or aliasing of an eq?

Post Thu Mar 26, 2020 7:19 am

vitocorleone123 wrote:
Thu Mar 26, 2020 7:11 am
So.... those aren't the Linear charts, those are the Harmonics. Intentional?
I think so :D I posted this one because of aliasing. Non of the eqs showed cramping.

User avatar
Burillo
KVRAF
3871 posts since 15 Nov, 2006 from Hell

Re: How to detect cramping and/or aliasing of an eq?

Post Thu Mar 26, 2020 7:19 am

both PTEq-x and Molot model saturation. can't have aliasing without harmonics, there's nothing to alias if the process is completely linear.
From Russia with love
Our online jams (if you speak Russian - you're welcome to join!)

User avatar
krabbencutter
KVRian
574 posts since 12 Jul, 2013

Re: How to detect cramping and/or aliasing of an eq?

Post Thu Mar 26, 2020 7:33 am

Most audio interfaces have a dynamic range from 110dB to 130dB at the line out. So everything that's happening well below (like -125dB) the 1kHz test signal won't even make it through the noise floor of your interface unless you compress the living sh*t out of it.
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Burillo
KVRAF
3871 posts since 15 Nov, 2006 from Hell

Re: How to detect cramping and/or aliasing of an eq?

Post Thu Mar 26, 2020 7:38 am

"compressing the living shit out of it" is usually the issue though. so many uses for creative squashing, as well as straight up distortion.
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User avatar
TB-ProAudio
KVRian
537 posts since 16 May, 2014 from Germany

Re: How to detect cramping and/or aliasing of an eq?

Post Thu Mar 26, 2020 8:43 am

resistent wrote:
Wed Mar 25, 2020 3:45 am
What are the options to detect cramping and/or aliasing of an eq without an dedicated analyzer tool?
Is it fine to run a 1khz sine into an eq and take a look at SPAN? Can I detect with this setup aliasing? Hows about cramping filters how to detect those? In fact I want to investigate to eqs which I think run into cramping/aliasing (test by ear :-) ). But maybe I fool myself. The eqs in question are EQ560 by RedRockSound and PTEq-X by IgniteAmps.

Thanks for any help.
You need a VST that creates continuous DIRACs (like MDA testtone), Span and a EQ that does decramping/oversampling (like dEQ12 or ProQ2/3) as reference. Set reference the EQ to bell/peak filter, frequency to 10kHz, gain to +24dB and Q to 0.7.

Place the DIRAC generator on track 1, route the output to track 2, place reference EQ there. Route track 2 output to track 4 (4 channels, channel 1+2).
Create track 3, place new EQ there with same settings as reference EQ, route output to track 4 (channel 3+4).
Place SPAN on track track 4 and enable display of all 4 channels, but you need to compare only channel 1 and 3.

This can be done very easily in Reaper. I hope this helps:-)

User avatar
resistent
KVRian
518 posts since 14 Apr, 2008 from Berlin

Re: How to detect cramping and/or aliasing of an eq?

Post Sun Mar 29, 2020 4:46 am

TB-ProAudio wrote:
Thu Mar 26, 2020 8:43 am
resistent wrote:
Wed Mar 25, 2020 3:45 am
What are the options to detect cramping and/or aliasing of an eq without an dedicated analyzer tool?
Is it fine to run a 1khz sine into an eq and take a look at SPAN? Can I detect with this setup aliasing? Hows about cramping filters how to detect those? In fact I want to investigate to eqs which I think run into cramping/aliasing (test by ear :-) ). But maybe I fool myself. The eqs in question are EQ560 by RedRockSound and PTEq-X by IgniteAmps.

Thanks for any help.
You need a VST that creates continuous DIRACs (like MDA testtone), Span and a EQ that does decramping/oversampling (like dEQ12 or ProQ2/3) as reference. Set reference the EQ to bell/peak filter, frequency to 10kHz, gain to +24dB and Q to 0.7.

Place the DIRAC generator on track 1, route the output to track 2, place reference EQ there. Route track 2 output to track 4 (4 channels, channel 1+2).
Create track 3, place new EQ there with same settings as reference EQ, route output to track 4 (channel 3+4).
Place SPAN on track track 4 and enable display of all 4 channels, but you need to compare only channel 1 and 3.

This can be done very easily in Reaper. I hope this helps:-)
Super. Nice explanation. Thanks.

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