I want to build a band-reject filter for the 60 Hz noise. So, I tried to use Butterworth filter to implement this specification. However, when I chose an order of 8, I got the following response, which makes sense.
However when I chose an order of 30. I got this weird response. Why is that?
The code to get the coefficient for the 8 and 30 order respectively is shown below
# fs = 200
b, a = signal.butter(8, [58 / (fs / 2), 62 / (fs / 2)], btype='bandstop')
b, a = signal.butter(30, [58 / (fs / 2), 62 / (fs / 2)], btype='bandstop')