Thursday, August 15, 2013


Well a bit more daydreaming and have been experimenting with a few ideas. I have always been fascinated by the MOTM 520 Cloud Generator VCO. It is a bit of an expensive beastie having an original price of $500 and no DIY option. That has become a bit easier with a DIY option for the E340 being offered but still $270 + postage and the $US Vs $AU is not in my favor at the moment... Anyway the aesthetic behind Forbin is not to spend much money, just to be unique and learn a bit so this represents my experiment with similar ideas. I have no real idea how they do it internally but I have prototyped up 4 sine wave oscillators with separate Brownian noise sources that modulate the 4 oscillators. The Brownian rate of change (well frequency I suppose -- Chaos Bandwidth in E340 parlance) and amount that it is tweaking each of the oscillators (Spread on E340) seem to all work fine. I want to make the number of oscillators also continuously variable rather than just stepped. I also need to do some thinking about a soft clipping arrangement Vs a an amplitude compression technique. I plan to rework this in Assembler after some of the prototype parts in C have been bashed out. The nice thing about the CortexM4F is that there are truckloads of floating point registers -- actually 32! so it is possible to leave a lot of the parameters in the CPU rather than loading them in and out of memory all the time... The sample frequency of this thing should be around ~150kHz to 200kHz so hopefully not too many artifacts will get through. It is pretty impressive what you can get out of a $7.99 evaluation board + a simple DAC!

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