[sdiy] simulate detune / polyphony with a single DCO

[rsdio at audiobanshee.com]

Hi Chris,

What you're describing seems to be hard sync, but with a irregular sync pulse from the control. I'm sure it would sound different from standard oscillator sync, but I doubt that it would actually sound like two notes. I suspect that you'll hear a timbre shift rather than two separate frequencies, but I haven't listened to any sort of simulation of what you describe. Have you actually listened to your circuit outside SPICE?

Your DCO integrator produces a ramp wave, I assume. In order to hear two notes, you'd have to either mix two independent ramp waves of different frequencies or produce a waveform that is the same as the mix of two waves. The problem is that your single DCO can only reset to a fixed position (0 V, I presume) in the ramp. It cannot jump to a non-zero voltage like the mix of two ramp waveforms would produce.

Then again, LFO control of the PWM input of a pulse/square waveform sounds about as rich as multiple oscillators, so perhaps your circuit will sound like multiple notes.

Let us know how it turns out!

I tried to get my analog synth to recreate what I think this would sound like, but it seems that the sync input either comes from the square wave oscillator output, regardless of settings -or- even PWMed waves still only sync on the rising edge, so the pulse width doesn't matter. If it were possible to insert a circuit that causes a sync reset on both rising and falling edges of the control waveform, then standard sync input could reproduce what you describe on both VCO and DCO modules.

Brian


On Apr 9, 2017, at 3:23 PM, Chris McDowell <declareupdate at gmail.com> wrote:
> 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?
>