The windowed sinc filter uses the inverse fourier transform of ideal low - pass filter frequency response. The Inverse transform of the ideal low - pass response is the sinc function (sinx/x). The inverse fourier transform of the required frequency response is taken and used as kernel a normal filter-The windowed sinc filter uses the inverse fourier transform of ideal low- pass filter frequency response. The Inverse transform of the ideal low- pass response is the sinc function (sinx/x). The inverse fourier transform of the required frequency response is taken and used as kernel a normal filter