filtering with mne_browse_raw/mne_process_raw

Hi,

I have a question regarding the filtersize (length of FFT) when
filtering the data with mne_browse_raw/mne_process_raw.
The user-interface version of mne_browse_raw does not offer to indicate
the filtersize, so I wonder what the default is?

Also, I wonder if there is any option within the mne stream to apply a
butterworth filter?

Thanks a lot,
Sarah