implementing a Patch function for notch filtering

[ahmadtourei]

It would be great to design a notch filter that can remove a narrow frequency band (such as power line noise at 60 Hz). As the processing will be carried out in the frequency domain and also the filter can be a pre-processing step for some data processing pipelines, we'd want to follow the behavior of Patch.whiten so the function can be applied on a DFT patch as well to avoid multiple DFT/IDFT. scipy.signal.iirnotch can be used under the hood.

[d-chambers]

Hey @ahmadtourei,

Really good idea!

ObsPy has a bandstop implementation that uses a Butterworth-type filter which Patch.pass_filter also uses. In fact, I started implementing a Patch.stop_filter a few years ago but never actually needed it in my research so I didn't finish it. Ideally, it should have exactly the same arguments as Patch.pass_filter but the frequency range specifies the stop, rather than the pass, band.

We could also do a Patch.notch_filter or Patch.irrnotch if you want to, as it is probably more stable (I guess) for removing very narrow frequencies. Both should be straight-forward to implement using examples already in the proc/filter.py module.

[ahmadtourei]

Sounds good! I'll work on it next week and get back to you @d-chambers.

[ahmadtourei]

closed by #448