[SciPy-user] filtering without phase shift

Stef Mientki s.mientki@ru...
Tue Jul 24 03:24:44 CDT 2007

Bryan Cole wrote:
> The easiest way to do non-phase-shifted filtering is to use FFTs i.e.
> FFT -> Low Pass -> iFFT
> The only reason to move to time-domain filters is if you must do
> filtering in real-time where the complete dataset is (yet) unknown and
> you must obey the laws of causality.
> Using a frequency domain filter, you can have whatever cutoff you like.
I'm a bit rusty, but isn't there a real danger by filtering in the 
frequency domain,
creating a rectangle cutoff in the frequency domain,
leads to an infinite ringing signal in the time-domain.

The normal way of getting zero phaseshift,
is to apply the filter twice, once normally and once in reversed order.

Stef Mientki

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