[sdiy] Why is Linear FM usually (always?) AC Coupled?

[mskala at ansuz.sooke.bc.ca]

On Sun, 2 Feb 2020, Pete Hartman wrote:
> I was just discussing this with a friend, and his speculation was that it
> would prevent any DC component from shifting the center of the modulation
> away from the note that was being played.  And while that seems plausible,
> I've never heard anyone explicitly say that was why.  To be fair I don't
> think I've heard anyone explain why.

Yes, I think that's the main reason.  People think that linear FM doesn't
shift the perceived pitch, and in order to help with that, it's common to
make the input AC coupled.

> And if so, why would Exponential FM be left DC coupled?  So you could
> transpose?

Yes, probably.  Exponential FM is usually just another resistor going into
the same summing node as the V/oct input (which pretty obviously needs to
be DC coupled), except through a pot so you can control the amount of
exponential FM.

-- 
Matthew Skala
mskala at ansuz.sooke.bc.ca                 People before tribes.
https://ansuz.sooke.bc.ca/