Sampling & Aliasing

A signal above half the sample rate does not vanish — it folds back and appears as a lower frequency that is indistinguishable from real data. 60 Hz mains sampled at 50 Hz looks like a 10 Hz wander you will chase for a week. The fix is an analogue filter before the converter, not maths after it.

Nyquist is the absolute floor, not a target — sample 5-10× your bandwidth for control loops so phase lag stays small. Filter order assumes a simple 20 dB/decade roll-off per pole.