I want to use high pass filter to filter frequency less than 100Hz. I use this code in python.
def butter_highpass(lowcut, fs, order=9): nyq = 0.5 * fs low = lowcut / nyq b, a = butter(order, low, btype='high', analog = False) return b, a def butter_highpass_filter(data, lowcut, fs, order=9): b, a = butter_highpass(lowcut, fs, order=order) y = lfilter(b, a, data) return y
and my signal after filter:
It show that some new frequency appear(from 200Hz -> 2000Hz). and I don't know why?. Can anyone explain why? Thank you