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 Forum index » Clavia Nord Modular » G2 Building Blocks
True anti-aliased user-definable waveform oscillator
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Tim Kleinert



Joined: Mar 12, 2004
Posts: 1023
Location: Zürich, Switzerland
Audio files: 6
G2 patch files: 212

PostPosted: Wed Mar 07, 2012 4:41 am    Post subject: True anti-aliased user-definable waveform oscillator
Subject description: Draw waveform of choice; accurate tuning
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Generating anti-aliased user-definable waveforms has been one of the remaining unsolved G2 problems.

I solved it yesterday. It's quite expensive DSP-wise, but from now on, if you really need user-definable waveforms, they are available.

You can draw your waveform of choice into the 16 step control sequencer. You can use the XFade step interpolation or deactivate it -the algorithm has no problem with the steep waveform flanks. If, you by any chance, still bump into aliasing, try lowering the frequency of the 36dB anti-alias filter. I tried it under many conditions and it should work the way it is though.

Also, this is the first DIY oscillator with perfect accurate tuning. The only caveat is that the circuit doesn't like ultra-fast and wide pitch modulations. It will still work, but the anti-aliasing will be compromised.

Nothing this red box can't do.

cheers to all,
Tim


EDIT: Warning! This circuit pushes the limits hard, and can malfunction on the demo software under certain conditions. The G2 hardware has no problem though.

EDIT2: Optimised version lower in the thread.


AntiAliasWave_TK.pch2
 Description:
True anti-aliased user-definable waveform oscillator; Draw waveform of choice; accurate tuning

Download
 Filename:  AntiAliasWave_TK.pch2
 Filesize:  2.55 KB
 Downloaded:  329 Time(s)


Last edited by Tim Kleinert on Wed Apr 04, 2012 1:09 pm; edited 1 time in total
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dorremifasol



Joined: Sep 28, 2006
Posts: 775
Location: Barcelona, Spain
Audio files: 7
G2 patch files: 47

PostPosted: Tue Mar 13, 2012 7:09 am    Post subject: Reply with quote  Mark this post and the followings unread

Tim, this is incredible. Thank you very much!

This was my most wanted feature on the G2, because I love small waveforms (did a lot of these in my Game Boy game soundtracks). I don't think I'll ever understand how you did it, but thanks again Smile

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Albert
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Tim Kleinert



Joined: Mar 12, 2004
Posts: 1023
Location: Zürich, Switzerland
Audio files: 6
G2 patch files: 212

PostPosted: Tue Mar 13, 2012 12:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

You're welcome. Sorry it's so DSP-expensive. If you don't need accurate tuning and pitch resolution, it can be economized considerably.
Also, if you intend to use this polyphonically, you can save some DSP by putting the waveform generator in the FX area and piping the audio and readout pointer back to the VA area via interslot.
Combining both these optimisations, it actually becomes surprisingly cheap DSP-wise.
As to how it works: In a nutshell, I'm constantly re-generating the waveform in a DIY sample memory array and preemptively cutting off the frequencies that would bounce back from Nyquist (alias) when playing back the waveform data at the desired pitch. The result is a pretty decent sounding wavedraw oscillator.
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dorremifasol



Joined: Sep 28, 2006
Posts: 775
Location: Barcelona, Spain
Audio files: 7
G2 patch files: 47

PostPosted: Tue Mar 13, 2012 1:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

No problems with the DSP usage, worths all of it. Thanks for the tips. I'm already having fun morphing between waveforms using the morphs and midi Smile

Some time ago I tried to emulate the so called Vowel-Consonant Synthesis used in the Casio keyboards of the eighties (I have an MT-68 and a CT-410V), but with the aliasing it sounded too ugly. Then I tried your previous method without tuning accuracy, but then it didn't worked very well either. Now I will be able to do it Very Happy

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Albert
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xav



Joined: Mar 21, 2005
Posts: 144
Location: paris
Audio files: 8
G2 patch files: 7

PostPosted: Wed Mar 21, 2012 5:01 am    Post subject: Reply with quote  Mark this post and the followings unread

Waw, Tim!
You are still giving us mor reasons to use that synth!
Thank you very much
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Tim Kleinert



Joined: Mar 12, 2004
Posts: 1023
Location: Zürich, Switzerland
Audio files: 6
G2 patch files: 212

PostPosted: Wed Apr 04, 2012 1:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've been able to optimise both the DSP usage and the modulation response.

This new design will respond faithfully to any kind of blue modulation signal without producing artifacts. (The old version had problems with modulo inter-/extrapolation overshoots when fast and wide modulations were applied). Also, it uses a tad less DSP.
I pushed the DSP load even lower by moving the waveform generator to the FX area, since it's a waste of DSP to calculate it more than once. Hence 2 interslot busses are used.

Cheers,
t

EDIT: Even more improvement, 2 modules less. Patch re-uploaded.


AntiAliasWave2TK.pch2
 Description:
True anti-aliased user-definable waveform oscillator; Draw waveform of choice; accurate tuning; VERSION 2 with improved modulation response and less DSP usage.

Download
 Filename:  AntiAliasWave2TK.pch2
 Filesize:  2.55 KB
 Downloaded:  327 Time(s)


Last edited by Tim Kleinert on Thu Apr 05, 2012 4:04 pm; edited 1 time in total
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dorremifasol



Joined: Sep 28, 2006
Posts: 775
Location: Barcelona, Spain
Audio files: 7
G2 patch files: 47

PostPosted: Wed Apr 04, 2012 3:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

Is there anything you can't do with this synth? Smile
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Cheers,
Albert
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Tim Kleinert



Joined: Mar 12, 2004
Posts: 1023
Location: Zürich, Switzerland
Audio files: 6
G2 patch files: 212

PostPosted: Wed Apr 04, 2012 3:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

dorremifasol wrote:
Is there anything you can't do with this synth? Smile


It doesn't do the dishes.

...Yet. Laughing
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