Aliasing

[1] In signal processing and related fields, aliasing is a phenomenon that a rebuild signal from the original signal's samples has low frequency components that aren't in the original one (i.e., if we sample too slowly, high frequencies appear as low frequencies, corrupting the data.), caused if the original signal has components at frequency exceeding a certain frequency called Nyquist frequency, fs/2, where fs is the sampling frequency (undersampling). That's due to 

[S1] To avoid aliasing, we must take (at least) twice as many samples per second as the highest frequency of interest, called Nyquist rate, named for Harry Nyquist.

• frequency of interest: highest frequency we care to capture capture accurately

  • of interest: what we care; that matters; attracts attention