It is well known that no time-limited signal is frequency-limited. So the frequencies of a time-limited signal extend upto infinity - may be decaying slowly or fastly in frequency domain. But we take signal's frequency content to be zero beyond some frequency and take that as the maximum frequency of the signal. My two questions are:
- Is there a solid fail-proof rule by which we can fix the maximum frequency?
- When the max freq is fixed and sampling is done, how do we guarantee that the infinite foldings that occur in frequency spectrum due to sampling, do not reinforce each other, at some particular frequency within folding frequency and distort the spectrum of the sampled signal?