[SciPy-user] filtering without phase shift

[Stef Mientki]

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