How to correctly apply bandpass filter to EEG data?

I have 25-electrodes EEG data, I used bandpass(myData, [0.5 40], 250) to apply a simple bandpass filtering on the data I have. I do not know why some time delay is exist after the application of the filter.

Answer 1

[Star Strider]

The bandpass function (and its friends) in my experience have all used filtfilt to do the actual filtering, so there should not be any delay or phase distortion.

You can check it with:

[myFilteredData, bpdf] = bandpass(myData, [0.5 40], 250); 

then:

myFilteredData2 = filtfilt(bpdf, myData);

and see if there is a difference when you plot them.

EDIT — (29 Oct 2023 at 21:58)

The bandpass function (and its friends) will always return an efficient elliptic filter if the 'ImpulseResponse','iir' name-value pair is added to the argument list:

[myFilteredData, bpdf] = bandpass(myData, [0.5 40], 250, 'ImpulseResponse','iir');

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