SV: [sdiy] Mopho modulation DAC configuration, update rate, etc

[karl dalen]

Tom Wiltshire <tom at electricdruid.net>:

> > Offcourse but there are basically no *modulation*
> frequency
> > limit within the PA397, it can go into audio frequency
> range
> > if one designs it in.
> 
> If the Mopho uses the same DCOs as the Prophet08, then I
> disagree, Karl. I might be wrong (happened lots before) but
> I don't see how you can do audio rate FM on a DCO.

Hehe, that was the kind of answer i suspected to see. :)
I was NOT talking about DCO FM, just the fact that the
PA397 are fully audiorate on it's modulations.

Lets examine the PA397, by first take away all the limited DsPIc stuff
then we have a chip thats very much like the 3396, now apply a 10khz
(random freq but high enough to create spectrums above nykvist just
for fun) to any control input within its defined range and you will
see that the PA397 will respond nicely.

Thats whats meant with audiorate modulations, it has nothing to do
what the DspIC can or canot do. You can for example AM the Mixer stage.
 
> Some people have argued that you can update the charging
> rate in the middle of a cycle without causing a glitch, by
> doing some recalculation of when the reset point would be,
> but I'm rather sceptical that it can be done accurately.

It's infact possible, replace the digitally generated tick
with a VCO and a parallel Expo that sinks current out of
the internal mirrors, now modulate the VCO and the expo and
viola, there you have PA397 VCO FM......................

Yes, i have tested it, and it's boring just the same ol'FM! :) 

But, again that's not what i initially meant.

Reg
KD


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