[Mne_analysis] low pass filter drop off

[Eric Larson]

Assuming you're using the overlap-add FIR filtering method (default) and
not the IIR method, it is designed in the frequency domain to minimize
energy outside of the pass band (i.e., above 45 Hz), yes. While I wouldn't
claim that the amplitude is reduced to being actually zero (except for
certain frequencies) due to ripple that occurs, it is reasonable to think
about the amplitudes above 45 Hz as being substantially reduced to some
value near zero (e.g., by 20+ dB relative to their original amplitudes).
The amount of signal in the stop-band that gets through depends on the
duration/number of samples of the FIR filter (as well as the shape of the
filter we build), which is why MNE will give you warnings about
insufficient stop-band attenuation when using short FIR filter lengths.

HTH,
Eric


On Mon, Oct 20, 2014 at 3:54 AM, Krieger, Donald N. <kriegerd at upmc.edu>
wrote:

>  Dear List,
>
>
>
> If the low-pass filter (mne_process_raw) is set to 40 Hz (default) with
> low pass width set to 5 Hz (default), does this mean that the amplitude of
> everything above 45 Hz is zero?
>
>
>
> Regards,
>
>
>
> Don
>
>
>
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