[Mne_analysis] low pass filter drop off

[Krieger, Donald N.]

Thanks, Eric.

Regards,

Don

From: mne_analysis-bounces at nmr.mgh.harvard.edu [mailto:mne_analysis-bounces at nmr.mgh.harvard.edu] On Behalf Of Eric Larson
Sent: Monday, October 20, 2014 12:29 PM
To: Discussion and support forum for the users of MNE Software
Subject: Re: [Mne_analysis] low pass filter drop off

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<mailto: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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