[sdiy] continuous tuning of analog oscillators

Brian Willoughby brianw at audiobanshee.com
Sat Jul 13 04:48:31 CEST 2019


On Jul 11, 2019, at 7:10 AM, ulfur hansson <ulfurh at gmail.com> wrote:
> also - in terms of generating waveforms digitally - i guess i’m much too enamoured with the alchemy of transistors, so it kinda takes the fun out for me... no gripes against digital at all though!!! i also do a lot of work in supercollider 😻

You can still use transistors for a DCO. Really, the acronym “DCO” is wrong, or at least incomplete. It’s really more like a VCO operating with hard sync from a DCO. If you have a transistor-based VCO that you like the sound of, then so long as it has a hard sync input then you can turn it into a DCO with very little sacrifice. Compared to a VCO with digital auto-tune, I can’t see how there would be any sacrifice at all.


> i wish there was a divide down technique that wasnt phase locked. maybe bernie hutchins phase modulation circuit could liven things up a little, but it would grow big quite fast and not really provide the solution im looking for…

Glad you brought up phase. I wasn’t thinking about that. However, all you need to do is allow the 16 timers to run independently without phase-locking them to each other. Yes, each VCO would be phase-locked to its digital timer for frequency accuracy, but there’s no reason that the 16 timers would need to be locked to each other.

You could even allow for variations like resetting the timer on each new note, or letting it free-run between notes and start with whatever phase happened when each new note is gated. You could even experiment with other sources that would reset the timer phase, other than Note On or pure free-running.


The only disadvantage I see for a DCO is that frequency is discrete, not continuous. You can make the steps in frequency really, really fine, but you can’t completely eliminate the stepping. In contrast, a pure VCO can be “in between” those discrete frequencies.

Brian




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