You don't need to do a fourier transform to measure a frequency, though. It doesn't really need anything special to measure the frequency of a 440 Hz tone to si

You don't need to do a fourier transform to measure a frequency, though. It doesn't really need anything special to measure the frequency of a 440 Hz tone to six digits or so given a single cycle. With some trickery you can get right down to 10-20 ps resolution, which would give you approximately eight digits from a single 440 Hz cycle. There is no frequency-domain effect here that would prevent you from measuring the time interval of a single cycle more accurately, except that it simply gets difficult on an electrical level when we are talking about resolving sub-ps intervals.