FW: Less stupid questions...

[Harry Bissell]

In practice the same A/D converter is multiplexed to all pots, and refreshed
so fast you don't notice... another plus is that in most cases we poor
mortals can only turn 2-3 knobs at the same time...

The Prophet V had only 127 levels (7 bit) scanning... This will definatly
give (*gasp*) the dreaded "Zipper Noise" when you move a pot...

There is a neat way to scan pots without a formal A/D converter... charge a
cap to a known voltage, discharge through an unknown R (the pot) and count
clock cycles until a comparitor says you have reached a certain discharge
point... If the cap is only discharges a part of the way, it can be somewhat
linear...

IMHO Zipper noise is the killer of all hybrid synth designs... The only one I
have ever heard without this "feature" is the Studio Electronics ATC (the one
with the membrane frontpanel and one big knob....) In this case its a rotary
encoder with no stops... so it doesn't matter where its "preset"

:^) Harry


Martin Gustafsson wrote:

> >    The polysix, yes the pots would HAVE to be scanned constantly
> > by the processor. say you load a patch with say a resonance of 0
> > but the pot is half way, why doesnt it jump? well the processor will
> > scan the pots and remember the values, it WONT apply them to the
> > current patch, it then constantly rescans them, if they differ from the
> > first value it applies that value to the current patch, if they are the
> > same as before (ie they've not been moved) then it ignores it.
> > cunning system really, but it means have a fairly decent quick settling
> > ADC to do this.
> >
> >    Paul
>
> I don't know about the polysix, but I think a simple RC-link and a
> comparator could be used to detect potentiometer changes and trig
> AD-conversion. That way you could use the same ADC for many pots without
> wasting processor cycles.
>
> Martin Gustafsson (new to the list)
> marguson at telia.com