I'm looking for a function whose frequency oscillates around a certain value (say, oscillating between 440 Hz and 880 Hz, at a rate of 1 Hz -- i.e., its frequency goes up and down once per second, preferably in a somewhat linear fashion).
I feel like it should be quite simple, but I'm having trouble coming up with such a function.
I tried $x(t)=\sin(\sin(t)\ t)$, but this doesn't seem to work, because it's not periodic -- I'm looking for something whose frequency goes up and down in a periodic fashion.
Ideas?