Frequency modulating a comb filter

[Medenka]

So here I am frequency modulating a comb filter, in Largo. And I am wondering - what is the FM doing to the comb, since a comb filter is a short delay, where Cutoff is delay length and Resonance - feedback depth.

For more clarity, the manual says:

The Comb filter types differ from the other filter types greatly, because they don’t actually damp any part of the signal, but instead add a delayed version of the input signal to the output.

[BertKoor]

Modulating delay length or feedback? With what? An LFO, Envelope, another control signal?
How fast are you modulating it, and at what depth?
So.. what does it sound like to you?

For more clarity, if the delay length is set to 2 ms (0.002 seconds) then I'd expect an input signal with a frequency of 1 / 0.002 = 500 Hz to be added upon itself, thus creating a resonance.

[DaveClark]

So here I am frequency modulating a comb filter, in Largo. And I am wondering - what is the FM doing to the comb, since a comb filter is a short delay, where Cutoff is delay length and Resonance - feedback depth.

For more clarity, the manual says:

The Comb filter types differ from the other filter types greatly, because they don’t actually damp any part of the signal, but instead add a delayed version of the input signal to the output.

While it is true that a 0 dB gain, delayed signal in isolation doesn't contain amplitude modifications of the original signal, the adding of a delayed signal on top of the original signal does cause modifications of the amplitudes of the frequency components, reinforcing some and diminishing others - not just producing resonances. That's how IIR (aka recursive) filters do their work.