Using a butterworth filter of order 2 with lowcut=8Hz and highcut=4Hz (bandpass) in an attempt to filter the 11Hz component, I get the following overall signal:
Now, of course, if I amplify this signal by 40 and plot it between -1s and 1s, I get the desired signal:
My question is what is causing these apparent "side lobes" in the filtered signal (second picture) at the left and right side? Is there a way to get around this? In the end, I want to subtract the filtered signal from the original signal, to remove this frequency. I can't do this, however, with the "side lobes."
These lobes also occur for order 3+ with lowcut=8 and highcut=14
These lobes also occur for lowcut=7 and highcut=15