I filtered my signal with low pass filter butterworth forth order with cutoff frequency of 50 hz. However when I compare the filtered signal with original one in frequency domain, it seems that the cut off frequency started from 25 hz instead of 50.
this is my matlab code and my data from here
%sampling frequency is 146 [b,aa] = butter(10, 50/146,'low'); data_filtered = filtfilt (b,aa,data);
did i make some mistake ?