Oscillator OUT->CV IN

I would like to “tap” the output of the oscillators to use as a modulation source for the CV ins (hack_me).
Looking at the schematics, I could take the audio signal before it goes into the CEM, at pin 8, after R13. Is that correct?

Oliver, I know you said that filter frequency modulation by the oscillators via the internal software wasn’t really possible (or, at least it wouldn’t sound good), but it would be possible via the CV ins (routed to filter cutoff), right?

Oh wait…dang. Am I right in thinking that, even if this was possible, the audio wouldn’t be amplified enough after R13 to adequately serve as a modulator?

If you want to do that, there are two things you need to take care of:

  • Make sure that the audio signal you sample is in the 0 - 5V range - that is to say, take it before the AC coupling capacitor.
  • Remember that what the AVR outputs is a PWM signal. The CV ins will only see 0 or 5V if it reads this as is. You need a RC filter to smooth the signal.

Also keep in mind that you’ll face the same problem than the one I described earlier: the modulation sources/destinations are refreshed only 1000 times per second, so whether you use a software routing, or the hardware routing you describe, the aliasing will be really severe and this will work only for lowish frequency audio signals.

I gave a shot at this modulation thing (audio output used, in software, as a modulation source), and it’s not that bad if you want fucked up sounds. It works best when modulating pulse width or any of the oscillators’ parameters. The funny things is the “wagon wheels” effect… For some notes which have harmonics (or a fundamental) close to the half of the refresh rate of the modulations (a bit below 31250 / 32 / 2 = 488 Hz), this harmonic/fundamental gets wrapped up to very low frequency because of aliasing, so this modulation behaves like a very low LFO. For some other notes, this is more FM-ish.

Interesting. Thanks for trying this out!