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Signal Processing

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    $\begingroup$ Is there any use to windowing the data before hand for a single-point DFT though? $\endgroup$ Commented Apr 11, 2013 at 22:10
  • $\begingroup$ @Mohammad Well you can view it as taking an N-point DFT for all N bins, and only looking at one bin. The question is then, is windowing important when taking a DFT? Well this depends on the application. No window = a rectangular window, which has a different frequency response to say a hanning window. In terms of magnitude response, different windows have different main lobe and side lobes characteristics. I imagine this is what you care about. See ccrma.stanford.edu/~jos/sasp/Spectrum_Analysis_Windows.html $\endgroup$ Commented Apr 12, 2013 at 9:56
  • $\begingroup$ @Dom I am familiar with the windowing process - what I am asking about is why one would care to window the original data signal, when you only care about 1 DFT bin. I dont think there are any advantages to that. The whole point of windowing is how it affects magnitude ratios among bins. Here though, we care about one bin only. $\endgroup$ Commented Apr 12, 2013 at 14:36
  • $\begingroup$ @Mohammad I think about each bin as a bandpass filter. So windowing alters the response of this filter to frequencies other than the one that it is tuned to (since we are smoothing the 'unwindowed' response with the DFT of the window). To make it clear, compare the magnitude response (20*log10(abs(X)) of a single bin as a function of different input frequencies (non-integer k values in the above code) for both a windowed and 'unwindowed' input sinusoid. $\endgroup$ Commented Apr 13, 2013 at 14:17