Feedback in FM synthesis

[Martin Czech]

:::Are you sure about this??

Yes , I'm very sure!

We have to decide between marketing bla bla and mathematics/physics.
This topic was allready discussed here.

All given formulas say so, as well as experiments.  Take some DX or TG
or SY. Take a two OP patch. Carrier fixed. Envelopes wide open. Sine
Wave selected. Now crank up the modulator, so that the sidefrequencys
are audible.  Now change modulator frequency, from dc to max.  It is easy
to hear that in the low end we percieve some frequency modulation, but
this gets weaker as the modulator sinks in freqeuncy. No frequency offset,
if we finally stop the modulator.  On the other hand sidefrequencys stay
constant loud if the modulator is moved-say- from 100 to 8000 Hz or so.



-> PM


The opposite would be observed for real FM.

Think of the practical implications of "stuck" modulators (because
of "fixed" or very low "ratio") in a chain, this would result in
frequency offsets.

With analog modules you will NEVER get the same sound palette as with
digital PM. Similar, yes, but not the same.
-most vco can not modulate through zero. This was widely discussed here
-most vco even don't have a linear input. The problems arising from
 this are discussed in E.N.
 
>From an engineering point of view, we allways think of phasors.
It is the easiest way, so PM, PD and "FM" is all really phase manipulation.
 
 
It would be interesting how all this PM<->FM confusion started.
I think it started with Chownings early work, the formulas say clearly "PM"
but Chowning seems not to be aware of this and wrote "FM".
He never discussed the differences. I don't know about Mr. Chownings
education, but communication theory may have not been part of it,
and that is where engineers usually discuss these topics,
because it matters for signal transmission etc.

m.c.