[sdiy] analogue DX-7-style Phase Modulation using quadrature signals ?

[René Schmitz]

Hi Jürgen,

> Now there will always be factors A(phi) and B(phi) such that
> sin(wt + phi) = A * sin(wt) + B * cos(wt).
> So we can modulate phi indirectly by modulating A and B
> with the right function, can't we?

IIRC this would be sin(wt + phi) = cos(phi) * sin(wt) + sin(phi) * cos(wt).

> I haven't done the maths for this, but probably A and B
> would be sin and cos functions of an arbitrary CV input
> signal to get the desired result.
> If so, all we need is a sin(x) and cos(x) nonlinear network
> which works over a certain number of periods.
> I think I remember from earlier discussions that there are chips
> that do this, and of course such a thing could also be implemented
> with diode networks etc.

Well such a sinewave network lets you already do phase modulation.

Suppose you have one for sin(x) with wide enough range, you would feed
it with a sawtooth which gives you a linear term, i.e. the wt in the
argument. Add the phi term directly to that and you would be there.
Admittedly there would be a discontinuity then.

Cheers,
  René

-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159