[sdiy] random thought about sine shapers

[David G. Dixon]

> Hmm, I'm not so sure it's the exact one I'm thinking of, because the
> one I am thinking off starts with 0% PW when the saw is output, and as
> we increase the setting, the slope of the (rising) saw to the left of
> the (negative slope) discontinuity has a 1% PW pulse there on top of
> it; then as we go further the saw is slowly faded out and on the other
> hand the PW gets higher until we reach 100%. I guess you could do
> this: feed the saw S to the pulse comparator, call the output pulse
> signal P. Have a voltage divider which divides evenly between the
> pulse comparator and 'no comparator'. Then those two signals get mixed
> together. I think it would/could work well this way. Note this allows
> you to have a sort of 'cs 80 style' saw there.

What you're describing is best accomplished with a cross-fader, I think,
unless I'm misunderstanding you.

> I might be wrong, but I believe an overdriven OTA sine shaper might be
> nicer in sound than an overdriven transistor sine shaper. Very long
> since I tried them, though, but the difference in sound is certainly
> there.

I've done both, and I see very little difference.  Simulation suggests that
one can achieve slightly better THD specs with a transistor-based one, but
we're talking about the difference between 0.5% and 0.7% or so.  IMHO, the
quality of the sine depends much more on the quality of the incoming
triangle than on the actual shaper itself.