[sdiy] "FM" Synthesis (was Re: Buchla 295 10-band comb filter topology)

[mskala at northcoastsynthesis.com]

On Sun, 27 Nov 2022, David G Dixon via Synth-diy wrote:

> The way you're describing it, phase modulation seems identical to frequency
> modulation.  Hence, I don't see the need for another term -- FM is
> sufficient.

I'm just waiting for someone to chime in saying that DC bias in the
modulating signal, magically propagating through the AC coupling capacitor
on the modulation input somehow, is a commonly-occurring and serious
disadvantage of "true" FM and is *the* reason both to choose PM instead
and to draw a distinction between the two.

In radio work, your FM signal is an FM signal regardless of whether you
modulate the oscillator (which oscillator? - there may be three or more in
a superhet transmitter, none of them operating at the final transmission
frequency) or pass part of the signal at some point through a modulator
that variably shifts the phase to create the modulation.  What matters is
the signal itself.

-- 
Matthew Skala
North Coast Synthesis Ltd.