[sdiy] Stereo Phasing With the 32 Stage MultiPhase Project

[scottnoanh at peoplepc.com]

Hey René,

> How are they controlled, are you again using an expo? (Well, I guess you
> do. And I guess I know how it would look. :-P) Yet the hypertriangle
> makes such a huge difference.

Yes, if you recall long ago, I breadboarded a phaser using VTL5C2's, but
used a linear transistor circuit for that.  You suggested an expo circuit,
and it worked wonders (I've been using the same circuit ever since).  Could
be that I need to re-examine that section to see if I've changed anything -
I, for example, replaced the tune trimpot with a fixed resistor.  In any
event, right now the hypertri does certainly seem to 'tighten' up the
sweeps, though it seems to wind the higher stages a bit too tightly - there
the normal triangle is easier to work out a good wide sweep.  A sine wave
works pretty well there too in some instances.

>
> > There's enough of a difference that,
> > with identical settings on each channel, there will still be a stereo
> > effect even if the channels are not modulated antiphase.
>
> I think with that many stages this is something one needs to live with
> to some degree, or else you need a huge pile of vatrols to select those
> 32 which have good pairing over the entire range.

Yes, I'll have to wait for my inheritance before I could try that =0).

> > I've got one nearly finished for the audio path - it just has a few
> > elements I'm not sure I want to keep or leave out.  The CV - ooooh,
> > not even started.  Right now I'm just using LFO's and a mixer from
> > the modular.  I'm running a triangle LFO through a FET distortion
> > circuit to get the hypertriangular wave.  Not sure if I want to stick
> > with that or try some other method.  In any case, 'inverted'
> > hypertriangular (keeping the timing anti-phase but preserving the
> > waveform) will require an inverted copy of the original triangle and
> > then distortion of that.
>
> I see the hypertriange simply as a transform that you put pre to one sum
> on the modulation inputs. And add those optional invertors prior to
> them. Maybe adding more signals before, or after them, since this is a
> nonlinear thing, that makes a difference of course.

That certainly makes sense!

Tonight I tried something I'd forgotten to do this weekend - I wanted to try
cross-regenerating the two phase sections.  It really turned out pretty
neat.  I haven't recorded a standard sweep, but I did post a very
interesting recording of it to my page here:

http://mypeoplepc.com/members/scottnoanh/birthofasynth/id18.html

Bottom of the page, under "Korg DW6000 Eaten By Phase Shifter" (if that
gives you any idea of the type of sample it is =-D).

Cheers,
Scott