Hmm thats what i got taught - (the Nyquist theorem) - but when i think about it, 2x doesn't seem enough. I might be wrong though ...
Either you are. or the entire world of engineers working in some way with sampling digital signals (including me) are
Heres why i think it's wrong
This is sampling at 2xf, yet the output is not what the input was.
That is what could happen at
the Nyquist frequency (highly theoretical though, since no circuit has a frequency deviation of exactly zero.
If your sample speed is a bit too low, you would get false readings (the input would appear to be of a lower frequency), but as long as your sample speed is just a wee bit higher than twice your signal frequency, you're in the green.
CD audio sample speed is 44.1 kHz and the signal can go to 20kHz - does your CD's sound bad? (Not talking music taste here of course