[sdiy] continuous tuning of analog oscillators

Tom Wiltshire tom at electricdruid.net
Wed Jul 10 23:50:26 CEST 2019

The “at least 16 micros to listen to all the oscillators at once” is exactly why most analog polys haven’t done it this way and have instead used an autotune routine that works out corrected DAC/CV values that the system can use to get accurate notes. Since (we assume) the behaviour of the oscillators is reasonably stable in the short term, you don’t *need* to be retuning continuously.

Since your “listeners” would have to know what frequency they were supposed to be seeing, they would have to be sent information about what the correct frequency was supposed to be, including any modulations. And presumably you’ve already got some “brain” in the synth that is already sending that information to a DAC to go to the voices, so now it has to send it to two places instead of one. Why not just use that brain to do the tuning correction at source rather than add it on as an afterthought. And that’s what an “autotune” routine is.


       Electric Druid
Synth & Stompbox DIY

> On 10 Jul 2019, at 22:02, ulfur hansson <ulfurh at gmail.com> wrote:
> hello list,
> I have a really nice synth voice up and running on my bench, and have always dreamt of making my own poly.
> all parameters are voltage controlled, but the tuning is... well... not perfect.
> currently I'm quite happy to omit oscillator FM, so in theory the oscillators would not "need" any modulation other than PWM.
> autotune feels a bit archaic at this point, so i'm wondering - a tiny microcontroller listening for zero crossings should be able to adjust the frequency of each oscillator for near perfect tuning, no?
> so far, i sadly haven't developed the skills required for digital solutions - but I wonder how crazy it would really be to implement something like this - can anyone think of a project / reading material that could help guide the way towards creating a tiny (preferably REALLY small) ADC/DAC listener circuit that could correct the resulting frequency of a sawtooth oscillator?
> it would be amazing to put 8 of these voices together with perfect tuning without any divide down or stepped interval solutions...... but then again it would also mean i'd need at least 16 micros to listen to all the oscillators at once!!
> any thoughts would be greatly appreciated, or even better yet - if someone would be interested in a collaborative effort, i'd be happy to send hand soldered smd prototypes between continents if necessary!
> many thanks,
> -úlfur
> -- 
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