[sdiy] simulate detune / polyphony with a single DCO

[Chris McDowell]

Thanks everyone for all of the great replies! 

My circuit actually does provide for a way to set what voltage the integrator resets to. I definitely had considered that this would be the main difference, and am glad to see everyone is on the same page. The micro I'm using has 3 DACs, and I'm using 2 of them for the input to the integrator (slope) and the reference voltage (ends up being reset voltage and a means for controlling charge direction). Since detuned triangles end up a trapezoid, it seems like that would be doable here, too. Anyway, multiple DCOs is certainly what will end up happening, but I'm having fun figuring out what sorts of embellishments are available here. 

Just tried all of this in Max, and the results are interesting indeed. For detuned sawtooths, it sounds like a variation on PWM, as it sort of "stops" at the two extremes. Still clearly a detuned saw feel, but the phasing isn't continuous. For other musical intervals, it sounds really great, especially when tuned with just intonation (which I had never really appreciated, heh). 5ths have an element of a sub octave going on (didn't think too much on why), and inharmonic intervals get very clangorous. Pretty satisfied! I'll post some results when I build up the module. 

Cheers, 
Chris 

> On Apr 10, 2017, at 12:11 PM, Tom Wiltshire <tom at electricdruid.net> wrote:
> 
> 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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