Re: [Discuss-gnuradio] FFT --> IFFT

[Martin Braun (CEL)]

On Mon, Nov 18, 2013 at 08:22:08AM -0500, Robert James wrote:
> Wow, switching to a rectangular window of fft_size solved it! I'm
> baffled: I know windows are a way of pretransforming the wave prior to
> FFT, to eliminate artifacts.  I just used the default window.  Why did
> I need a rectangular window here? In what other cases do I need it?

If you want to keep all the properties of the signal, you need a rect
window. What you did was: apply a window, then do an FFT, apply the
window again, do an IFFT. Obviously, you're distorting the signal
every time you do the (I)FFT. A boxcar window won't change the signal.

For spectral analysis or filter design, you typically use other windows.

MB

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