Page "Fourier analysis" Paragraph 62

Conversely, when one wants to compute an arbitrary number ( N ) of discrete samples of one cycle of a continuous DTFT, it can be done by computing the relatively simple DFT of s < sub > N </ sub >, as defined above.

In most cases, N is chosen equal to the length of non-zero portion of s. Increasing N, known as zero-padding or interpolation, results in more closely spaced samples of one cycle of S < sub > 1 / T </ sub >( ƒ ).

Decreasing N, causes overlap ( adding ) in the time-domain ( analogous to aliasing ), which corresponds to decimation in the frequency domain.

( see Sampling the DTFT ) In most cases of practical interest, the s sequence represents a longer sequence that was truncated by the application of a finite-length window function or FIR filter array.