An infinitely long sinusoid has a Fourier transform that is non-zero at only one frequency. Multiplying that sinusoid by any window function is a non-linear operation that always creates new Fourier transform components. That is "leakage", whether or not the number of cycles in the window length is an integer. If that Fourier transform is a sinc function (rectangular window) and we sample it at only the main lobe and the zero-crossings, then we will see the illusion of no leakage. But we will be quickly disillusioned when we apply that rectangular window to our sinusoid embedded in a summation of other signals.
Bob K
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