[SciPy-user] filtering without phase shift

Bryan Cole bryan@cole.uklinux....
Tue Jul 24 02:14:25 CDT 2007

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.



On Mon, 2007-07-23 at 22:27 -0500, Ryan Krauss wrote:
> I have a vector of data from an impact test.  The data has some
> "noise" in it that is really ringing in the mass used in the test.  I
> have spent a fair amount of effort getting rid of the ringing or
> trying to design the test so that the ringing is at as high a
> frequency as possible.  I now must resort to filtering the data.
> I can get fairly decent results with a 10 kHz filter (see attached).
> But I can get really nice results with a 1 kHz filter and then
> shifting the vector back in time - somewhat arbitrarily.  This feels
> slightly unscientific.  I googled for zero phase filters, but don't
> really understand what I was reading.  Is there a way to get magtitude
> attenuation without phase lag that is easy to implement and accepted
> as good practice among signal processing experts?
> Thanks,
> Ryan
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