Weighting factors overwhelming majority of the known windows for the discrete Fourier transforms (DFT) is calculated using simple approximation functions. How differ characteristic "exact" and "approximated" windows? We study the problem of the weighting factor differences of coefficient values and parameters of "exact" and "approximated" weight windows for DFT. Designed 2-term approximation function for 2x-windows of Chornoborodovs. It is shown that for the 3x-window of Chornoborodovs not there exists a 3-term function approximation, since this approximation gives the deterioration of the side lobe level to 20 dB.
Discrete Fourier transform, weighting function, filter, sidelobe level