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 Forum index » Clavia Nord Modular » Nord Modular G2 Discussion
Nord G2's allpass filter behaviour is odd?
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jaffasplaffa



Joined: Sep 21, 2010
Posts: 23
Location: denmark
G2 patch files: 2

PostPosted: Sat Sep 10, 2016 1:29 am    Post subject: Nord G2's allpass filter behaviour is odd? Reply with quote  Mark this post and the followings unread

Hello Smile

I have been playing a bit with Nord G2's allpass filter(the multimode filter set to 6db and use BP output). But from how I understand allpass filter and how I have used them before, it doesnt really act like an allpass filter. Something odd is going on.

I have been trying to create a good old Schröeder/Gardner stylish reverb, using delay lines and all pass filters and I have successfully created those on an Axoloti DSP synth. But when i try to make the exact same circuits on G2, the allpass filter is behaving weird. As soon as you start feeding the allpass back into itself(which is necessary for reverb creation), it just starts to resonate in a manner that basicly just sounds like a regular filter where you crank the resonance to max; the resonance creates a tone and basicly destroy what ever sound you put through it. Nothing reverb like comes out of it, like it should it just resonates like crazy. The circuits I build on Axoloti DSP works and rebuilding it on Nord G2 doesnt.

So I am pretty sure there is something weird going on with the allpass filter.

Have anyone else played around with the allpass filter on G2 an experienced odd behaviour?

Thanks
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Tim Kleinert



Joined: Mar 12, 2004
Posts: 1148
Location: Zürich, Switzerland
Audio files: 7
G2 patch files: 236

PostPosted: Sat Sep 10, 2016 4:47 am    Post subject: Reply with quote  Mark this post and the followings unread

The G2 SVF in allpass mode does indeed have unity gain issues, probably because of the way the integrators work in a SVF topology (only conjecture, would have to tinker to be sure).

Use this building block instead. (Since the SVF also eats 3 outputs, it's not more expensive.)

cheers,
t


6dB_allpass.pch2
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jaffasplaffa



Joined: Sep 21, 2010
Posts: 23
Location: denmark
G2 patch files: 2

PostPosted: Sat Sep 10, 2016 6:24 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey Tim Smile

Thank you for the suggestion. I'll definitely try this out tonight when I get home Wink
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