ca 4 pole filter , fake or not

The Cherry Audio CA2600 is a powerful, self-contained duophonic synthesizer inspired by the groundbreaking ARP 2600 synthesizer.
gentleclockdivider
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ca 4 pole filter , fake or not

Post by gentleclockdivider » Mon Nov 02, 2020 4:02 pm

Just a simple question and a n honoust ansewer
I suspect that the resonant peak in the 4 pole filter is just an added sine wave (tuned to filter freq .) and not the result of a feedbacking filter .
The resonant peak is just too narrow and it is located slightly above the cut-off frequency , I've had a lot of synths but have never actually seens this kind of peak before .
Sure is some some actual real resonance going on ( see screenshot ) , but that narrow peak looks verry strange
Image

And here I've done the same in reaktor ( without actual real resonance ) .
Image
Image
I am pretty sure the r(extra narrow )esonant peak is faked , I can get there 99% close with 20 year old reaktor primary modules , behaving under the exact same circumstances .
My theory is that the 2pole is using real resonance , the 4pole is 2 pole ins series ( so also a bit of real resoance ) but automatically engages a sine osc .
I am almost sure about it , the filter just behaves too weird and I can get it to replicate it exactly with standard primary modules
I would really like a answer from cherry audio

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cherryaudio Greg
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Re: ca 4 pole filter , fake or not

Post by cherryaudio Greg » Mon Nov 02, 2020 6:09 pm

Hi,

I don't know the details of the inner workings of the filter, but I passed your comments along to the software developers.

Greg

gentleclockdivider
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Joined: Mon Nov 02, 2020 3:57 pm

Re: ca 4 pole filter , fake or not

Post by gentleclockdivider » Tue Nov 03, 2020 3:32 pm

Any news on this ?
Here are two files , both files contain a cherry audio and reaktor ensemble audio file , with stock primary modules using a sine wave for fake resonance
Thy sound verrry close , to close to consider the CA2600 be analogue modelled at all , given the fact I used 20 year old primary modules and fake resonance

https://app.box.com/s/o5q0etf24dl9acrgvb1fhv9feldno2mv
https://app.box.com/s/ksu4a78fg6oi9axd6tx4frx5j7twvqs5

gentleclockdivider
Posts: 39
Joined: Mon Nov 02, 2020 3:57 pm

Re: ca 4 pole filter , fake or not

Post by gentleclockdivider » Wed Nov 04, 2020 7:17 am

bump

dergundel
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Joined: Wed Nov 04, 2020 2:47 pm

Re: ca 4 pole filter , fake or not

Post by dergundel » Wed Nov 04, 2020 3:17 pm

Hello gentleclockdivider,
good finding!
I can confirm this strange behaviour of the filter. I compared high resonance settings with Arturia’s ARP2600 V3 and WayOutWare’s TimewARP 2600 just feeding a simple sawtooth into the filter. Sweeping the filter you typically get a reinforcement of the partials. Both Arturia’s emulation and TimewARP do show this behaviour, while CA2600 doesn’t, there is just some kind of beating when the presumedly added sine wave and the gentle resonance peak is passing the partials.
Hope we hear from cherry audio soon.

gentleclockdivider
Posts: 39
Joined: Mon Nov 02, 2020 3:57 pm

Re: ca 4 pole filter , fake or not

Post by gentleclockdivider » Wed Nov 04, 2020 5:06 pm

Could you post a screenshot of the spectrum analyzer of both timewarp/arturia , so we can compare
-resonance 80 ( just make sure there is an obvious spike )
-freq 4Khz (non kbd tracked ) ,4 pole filter
-osc 3 set to 16' , disable kbd

Thanks

dergundel
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Re: ca 4 pole filter , fake or not

Post by dergundel » Wed Nov 04, 2020 6:47 pm

Hi, I tried my best. Both synths behave a bit different, but you can clearly see, that there is a considerable resonance peak (at 90% with Arturia and about 70% with TimewARP) but it is building gradually around the cutoff frequency, getting steeper and steeper as the resonance is increasing. There is no singular spike whatsoever.
Hope this helps.
Best.
Attachments
TimewARP2600 res 70 .jpg
TimewARP2600 res 70 .jpg (266.08 KiB) Viewed 695 times
Arturia res 90.jpg
Arturia res 90.jpg (232.83 KiB) Viewed 695 times

gentleclockdivider
Posts: 39
Joined: Mon Nov 02, 2020 3:57 pm

Re: ca 4 pole filter , fake or not

Post by gentleclockdivider » Wed Nov 04, 2020 7:44 pm

Thanks
I will use your images for reference and point them to this thread



https://www.kvraudio.com/forum/viewtopi ... 2#p7932022

gentleclockdivider
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Re: ca 4 pole filter , fake or not

Post by gentleclockdivider » Wed Nov 04, 2020 11:54 pm

Still waiting for one of the developers to chime in , why so quiet ? :mrgreen:

Cherry Dan
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Re: ca 4 pole filter , fake or not

Post by Cherry Dan » Thu Nov 05, 2020 12:35 am

Thanks for your interest in our products. I can assure you that we are as interested in getting these details right as you are in analyzing what we've built, and I commend you for your dedication to this issue.

There was indeed a small math issue in the CA2600's filter code that caused the weird resonance peak that you observed. Sonically it was correct but the filter was not behaving as it should. We've just published CA2600 Build 86, which will automatically update the next time you run CA2600 (unless you've turned off automatic updates). Build 86 features improved filter code that correctly self-oscillates.

Please let us know how Build 86 works for you!

Thanks,
- Dan @ Cherry Audio

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