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 Forum index » Clavia Nord Modular » G2 Building Blocks
Trivial oscillators
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Tim Kleinert



Joined: Mar 12, 2004
Posts: 1147
Location: Zürich, Switzerland
Audio files: 7
G2 patch files: 236

PostPosted: Wed Nov 23, 2016 5:09 pm    Post subject: Trivial oscillators
Subject description: Forcing stock G2 oscillators to generate trivial non-bandlimited waveforms
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Hi,

Long time ago I made the (baffling) discovery that signals hitting the FM inputs of stock G2 oscillators were ignored by their internal band-limiting (anti-aliasing) processes.

What I discovered just lately is that, by dialing an oscillator into 0Hz mode, using FM Track mode and an accurately scaled fixed FM offset, one thus can force a stock G2 oscillator module to generate its waveform naively, meaning without any bandlimiting (anti-aliasing).

Of course this isn't at all useful when utilizing bespoke oscillator as a primary audio source. However, when using it to drive a nonlinearity in order to obtain new waveshapes, the non-bandlimited version performs much cleaner and better, as it doesn't contain the added BLEP/BLAMP residuals which generate unwanted artifacts when processed through the nonlinear waveshaper.

The attached building block patch contains a comparison scheme, which clearly demonstrates the audible advantage of a non-bandlimited G2 sawtooth oscillator over a bandlimited one when driving a control-sequencer used as a fiercely nonlinear waveshaper.

This discovery also renders obsolete my building block deriving a non-bandlimited audio-rate sawtooth from a sawtooth LFO via audio-rate inter-/extrapolation, because it's obviously way simpler and cheaper to use a stock sawtooth oscillator set up as demonstrated in the patch here. Hence quite a few of my previously published patches, which use sawtooth LFOs in the aforementioned manner, could be improved accordingly. Embarassed Ah, "there is no end to learning". (-Robert Schumann)

cheers,
t


TrivialOsc____TK.pch2
 Description:
Forcing stock G2 oscillators to generate trivial non-bandlimited waveforms

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 Filename:  TrivialOsc____TK.pch2
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jamos



Joined: Jun 01, 2004
Posts: 495
Location: Eugene, Oregon, USA
Audio files: 4
G2 patch files: 39

PostPosted: Sat Nov 25, 2017 12:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

Tim, I have to admit... I can't hear any significant difference between the two versions. Both have substantial aliasing artifacts. Is there an error in the patch??
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Tim Kleinert



Joined: Mar 12, 2004
Posts: 1147
Location: Zürich, Switzerland
Audio files: 7
G2 patch files: 236

PostPosted: Tue Nov 28, 2017 5:00 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Jamos,

I don't own a G2 anymore, but the patch performs as intended on the demo version.

Both versions will exhibit aliasing since the whole process of using an unipolar sawtooth oscillator to read out of a control sequencer isn't bandlimited. However, forcing the oscillator to generate its sawtooth naively as demonstrated in the patch will produce a cleaner result.
Using a control sequencer as a waveshaper probably isn't the best example because of the lack of bandlimiting as mentioned. However if you use a 0Hz PhaseMod sine oscillator as a sine waveshaper and drive it with the correct mod range, the difference becomes night and day. Using a "normal" sawtooth (bipolar this time) as the modulator will exhibit artifacts generated by the bandlimited flanks. The trivial one will generate a pure and perfect sine.
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jamos



Joined: Jun 01, 2004
Posts: 495
Location: Eugene, Oregon, USA
Audio files: 4
G2 patch files: 39

PostPosted: Wed Nov 29, 2017 6:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

OK Tim, I'll give that technique a try. Thanks.
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