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 Forum index » Clavia Nord Modular » G2 Building Blocks
Octave Phase Coherent Sawtooth Oscillator
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Tim Kleinert



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

PostPosted: Sun Apr 17, 2011 1:10 pm    Post subject: Octave Phase Coherent Sawtooth Oscillator
Subject description: for that "divide down" polyphony sound of string machines
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Another thingie I found in my "patch vaults".

It's a solution to the problem of polyphonic octave-phase-coherent oscillators, as produced by the "divide down" technique in vintage string machines and organs. The topic has turned up here and there in the discussion of Solina and organ emulations and there didn't seem to be a solution. It seemed to be one of those "things the G2 can't do".

Rather than dividing down, this patch "multiplies upwards" from 12 base oscillator phase driver sawtooth LFOs residing in the FX area, which are multiplexed back to the voice area via inteslot busses. Here they are demultiplexed and processed by nested modulo circuits controlled by the keyboard, and drive the phase of a 0Hz sine oscillator (resetted at patch load). Feedback is added to this phase modulation to generate a quasi-sawtooth with controllable brilliance. The result is a sawtooth oscillator with static phase relationship within octaves. Due to calculation limitations, the frequency range is limited to 7 octaves, starting at C2. For musical purposes, this is sufficient.

The phase drivers clock at control rate. At first I upsampled them to audiorate (via linear interpolation), but the considerable additional DSP load didn't seem worth it. It sounds fine as it is.

Deriving a sawtooth wave is only one possible application. Triangle and Square are also possible. Multiple organ drawbars are more of a problem, because the range of possible oscillator frequencies is limited by calculation boundaries of the Clavia system and aliasing problem. However, there might be a workaround here, I'll have to give it another thought.

However, here's another limit pushed. Smile

cheers,
t
EDIT: This design is obsolete. Check out this:
http://www.electro-music.com/forum/post-358184.html#358184


OctPhaseCohOscTK.pch2
 Description:
for that "divide down" polyphony sound of string machines

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 Filename:  OctPhaseCohOscTK.pch2
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Last edited by Tim Kleinert on Thu Apr 05, 2012 1:39 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: Sun Apr 24, 2011 2:49 am    Post subject: Reply with quote  Mark this post and the followings unread

Nice!
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Cheers,
Albert
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