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Re: fftw and derivative. once again

Started by Jerry Avins January 9, 2011
On Sunday, January 9, 2011 6:52:09 PM UTC-5, Tim Wescott wrote:

  ...

> You're not using any frequency limiting -- are you sure you're not just > amplifying the heck out of your noise? > > In Scilab: > > -->N = 4096; n = 0:N-1; > > -->nn = pmodulo(n + N/2, N) - N/2; > > -->x = exp(-nn.^2 / 100000); xd = ifft(fft(x) .* (-nn .^ 2)); > > -->clf; plot2d(n, [x' xd']) > > gives me what looks like a very clean double derivative of the input > Gaussian.
I suppose the double differentiation simply negates the signal, avoiding the need for phase shifts. Jerry