""…all methods of modulating a wave can be recontextualized as frequency modulation!" That's the classic way to think about it. Another way is to view the inpu

""…all methods of modulating a wave can be recontextualized as frequency modulation!" That's the classic way to think about it. Another way is to view the input as simply a sequence of voltage readings." Right. And modulation of any type produces sidebands as per Fourier! Do anything whatsoever to disturb a pure sine wave then math and physics dictates it so.