[regularfry]

Every non-linear mixing of signals gives you sum and difference frequencies. It's less a weird PLL thing and more a weird trig function thing.

[kayson]

Its not even a non linear thing. Its a sampling thing. Even ideal sampling exhibits aliasing.

https://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampli...

[regularfry]

Yes, and. You can look at aliasing as a special case of heterodyning. Sampling is a nonlinear mixing.