i created a bandstop filter to remove noise from a noisey ecg 70 - 90Hz. see psd:
The filter works well - when i look at ecg back in the time domain its very clear, but i am just confused as to why there is a dip between 75-85hz?
thanks for your help.
fs = 200;
Wn = [65*2/fs,90*2/fs];
deg2 = 6;%filter deg
[B,A] = butter(deg2,Wn,'stop');
filteredSignal = filter(B,A,filteredSignal1);