[Mne_analysis] Low pass filtering questions

Alexandre Gramfort gramfort at nmr.mgh.harvard.edu
Thu Mar 14 08:30:42 EDT 2013
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hi Don,

> Please bear with a further question:
> If the low-pass is set at 40 Hz, then the cos^2 drop off is applied beginning at the 40 hz components and falling to zero at 45 ?  Or is it applied beginning at something like 38 hz so that the fourier coefficients are attenuated by a fact of 2 at 40 ?

I am not 100% about the C code but I bet for 40 to 45 with 0 at 45 Hz

> And pardon this stupid question: Does this produce a gain of 0.0 for all higher frequencies in the filtered signal above 45?  Or is there some kind of ringing which occurs?

it does remove all frequencies about 45Hz up to some numerical errors
and if there is some ringing it will be in time. The less the stop
band (here 5) the more ringing in time domain.

Alex



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