Frequency modulation.

Audacity Help Forum Windows
1

How do I make a tone of 440 Hz with a modulation of 5.5Hz and a deviation of 1/13 of the base?

2

I think your’e missing a value. You want it to switch between values like Frequency Shift Keying, or sine modulation like a broadcast transmitter? I don’t think we can do either one, but it’s good to know.
Koz

3

Try this code in the Nyquist Prompt effect (http://manual.audacityteam.org/o/man/nyquist_prompt.html):

(setf fc 440.0)
(setf depth (/ 1.0 13.0))
(setf modHz 5.5)

(let ((mod (mult depth fc (lfo modHz))))
  (fmosc (hz-to-step fc) mod))