[sdiy] simulate detune / polyphony with a single DCO

[Tom Wiltshire]

You could also have a look at the various variations of Bernie Hutchin's Sawtooth animator circuit.
Here's the original:

	http://electronotes.netfirms.com/AES4.PDF

The very simple and very clever trick is to add a variable-width pulse wave to the ramp to produce another ramp with a phase shift. Since a varying phase shift is a vibrato, you can get a detuned ramp by feeding an LFO to produce the variable-width pulse wave. Repeat several times to taste and you've got a fully-analog supersaw sound.

This turned up recently in the Yves Usson designed Arturia Minibrute:

	http://hackabrute.yusynth.net/index_en.php

(Have a look at the "super saw" schematic.)

This would work just as well with a DCO. You could potentially produce the variable-width pulse waves within the same uP that's producing the ramp reset pulses, which then saves you an LFO and a comparator per-extra-osc.

HTH,
Tom

On 9 Apr 2017, at 23:23, Chris McDowell <declareupdate at gmail.com> wrote:

> 
> Howdy list, 
> 
> I've been playing with DCOs, and am realizing that detune or even polyphony (which would end up paraphony I guess) could be achieved with a single DCO. The idea is to use two timers in a microcontroller, pulsing the same pin that's used to reset the DCO's integrator. A built in DAC from the micro controls the rate of the integrator, and as detune increased, would adjust the slope. I have a PCB on the way to test all this out, looks good in LTSpice. 
> 
> Anyone heard of this being done before? Are there any glaring dumb oversights?
> 
> Cheers! 
> Chris 
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