fft lowpass filter trouble

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1

Hello,

My name is Karen. I am an undergrad student doing research in Dr.
Stufflebeam's lab.
I am trying to use the fft lowpass filter (<8 Hz) in MNE Matlab toolbox to
eliminate the ringing in MEG data.
However, I kept getting error "Filter order must be a real, positive
integer".
data=fftlowpass(left_13_30,Fs,8,9);
This is the matlab code I used, where left_13_30 is the data to be filtered,
Fs is the sampling frequency, 8 Hz is the passband and 9 Hz is the stopband.
I tried to increase the stopband to 20 Hz, but it still doesn't work.
Thanks a lot for your help!

Best,
Karen
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2

Hi Karen,

I did not find fftlowpass in the mne matlab folder.

What is the length of your data,

Rule of thumb for good filtering your data length should be atleast 3 time
or higher than the filter length.

Sheraz