[sdiy] MIDI VCO Control - but not CV?

[cheater cheater]

>  Chortle chortle! Don't you see that what you've just done here is build a
> PWM DAC to generate a CV for a standard VCO!

Indeed a PWM DAC it is, I know :)

Harry: the filtered idea is just for a 'PWM DAC' sort of circuit. I
think this wouldn't have a lot to do with the feedback idea.

Regarding feedback steering:
you could do something like this:
look at the last two cycles,
compare them to the pitch,
and heighten or lower the CV by a small bias to make the pitch correct.
Repeat after that.
There's no transient distortion as there's no CV - just normal sync.

Cheers
Damian

On 7/15/08, Tom Wiltshire <tom at electricdruid.net> wrote:
> Damian,
>
>  On 15 Jul 2008, at 14:22, cheater cheater wrote:
>
>
> > OK, so:
> > in a DCO, the trigger pulses basically replace the comparator.
> > In a CV FM VCO, the CV controls the current going to the accumulator.
> >
>
>  Yep, that's it!
>
>
> > This indeed could be problematic to put together.
> >
>
>  Hey, no-one said it'd be easy!
>
>
> > What if you use the pulses to create a DC CV? Take the pulses and put
> > them through a reeaaalllyyy strong LPF. Sort of like a DSD DAC. Then
> > you get DC voltage, dependent on how many pulses you have per second.
> >
>
>  Chortle chortle! Don't you see that what you've just done here is build a
> PWM DAC to generate a CV for a standard VCO!
>  This is a perfectly valid and effective approach, of course (Prophet 5 is
> just one example that works this way), but it's not a DCO and it's not
> avoiding a MIDI2CV convertor - in fact, it IS a MIDI2CV convertor.
>
>
> > The problem here is to have this voltage respond to note-ons without
> > lag. However, if you want your keyboard to have a range from 10 Hz up
> > to, say, 24000 Hz (I would say that could satisfy even the best
> > 'golden ear'! :^) ) you could still output the pulses quickly enough
> > to be able to complete the cycle several thousand times a second.
> >
>
>  Yes, you're right to spot the pitfalls of a PWM DAC. There are other
> designs that would work much better.
>
>  Regards,
>  Tom
>
>