[SciPy-User] Amplitude scaling in fft

Sharaf Al-Sharif sfalsharif@gmail....
Thu Jan 21 13:09:25 CST 2010


Thank you for your answer.

Sharaf

2010/1/19 Jochen Schroeder <cycomanic@gmail.com>

> Hi,
>
> your answer doesn't really have a clear answer. Say raw_fft/raw_ifft is an
> fft
> without normalization then:
> A = raw_ifft(raw_fft(a, n=2**11), n=2**11)
> A = N*a
>
> where N=2**11 not len(a). However numpy does perform a normalization step
> in
> the ifft part, so that
> numpy.fft.ifft = raw_fft / N
>
> This way we can use the fft just as a Fourier transform and also
> fft(\delta) is
> constant 1.
>
> Hope that explains things a bit.
>
> Cheers
> Jochen
>
>
> On 01/17/10 23:44, Sharaf Al-Sharif wrote:
> > Hi,
> > I'm a bit confused regarding how the amplitudes returned by np.fft.fft
> (or
> > np.fft.rfft) relate to the amplitudes of the original signal in time
> domain.
> > If:
> > A = np.fft.rfft(a,n=2048)
> > but,
> > n_pts = len(a) < 2048,
> >
> > will the physical amplitudes in time domain be np.abs(A)*2/2048 , or
> np.abs(A)
> > *2/n_pts? Or something else?
> > Thank you for your help.
> >
> > Sharaf
>
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