[sdiy] Digital pots as the gain element in a filter

[David G Dixon]

> And no, I don't know of any other synth designs using 
> digipots for the filter control element.

I was in a music store a couple of months ago, and spent some quality time
with some Roland or Korg keyboard or other.  I can't remember which one it
was, but I think it might have been the Roland GAIA.  Anyway, it had a
decidated filter cutoff knob on the panel.  If you swept this knob while
holding down a note, it swept the cutoff in digital steps, and as with most
filters, the useful range of cutoff didn't cover that much of the knob
rotation.  Hence, there were actually very few digital steps within the
useful cutoff range, such that twiddling the knob back and forth over this
range actually sounded a bit like LFO-driven sample-and-hold control of the
cutoff.

So, based on that experience, I would say that some production synths use
digital pots as filter control elements.  And it's pretty darn crappy!