I am trying to filter ECG signal acquired from Bioplux sensor. I am including lowpass filter to remove noise of frequencies over 200 Hz, highpass filter for removing baseline wander, and notch filter for removing powerline frequency of 60 Hz. I am not able to understand why I am getting a wavy shaped output after the high-pass filtering. Could someone suggest some ideas to get properly filtered ECG signal? The rawsignal data text file and the obtained output after filtering can be seen in the following link: https://drive.google.com/open?id=1hvvQpMMa_hn9VNlUh4HAqb_H1lCu70or The code I have written is as below: from scipy import signal from scipy.signal import butter, iirnotch, lfilter import numpy as np import matplotlib.pyplot as plt def butter_highpass(cutoff, fs, order=5): nyq = 0.5*fs normal_cutoff = cutoff/nyq b, a = butter(order, normal_cutoff, btype='high', analog=False, output='ba') return b, a def butter_lowpass(cutoff, fs, order=5): nyq = 0.5*fs normal_cutoff = cutoff/nyq b, a = butter(order, normal_cutoff, btype='low', analog=False, output='ba') return b, a def notch_filter(cutoff, q): nyq = 0.5*fs freq = cutoff/nyq b, a = iirnotch(freq, q) return b, a def highpass(data, fs, order=5): b,a = butter_highpass(cutoff_high, fs, order=order) x = lfilter(b,a,data) return x def lowpass(data, fs, order =5): b,a = butter_lowpass(cutoff_low, fs, order=order) y = lfilter(b,a,data) return y def notch(data, powerline, q): b,a = notch_filter(powerline,q) z = lfilter(b,a,data) return z def final_filter(data, fs, order=5): b, a = butter_highpass(cutoff_high, fs, order=order) x = lfilter(b, a, data) d, c = butter_lowpass(cutoff_low, fs, order = order) y = lfilter(d, c, x) f, e = notch_filter(powerline, 30) z = lfilter(f, e, y) return x return y return z rawdata = np.loadtxt('D:\CANADA TRIP\BiosignalsSample.txt', skiprows=0) signal = rawdata fs = 1000 cutoff_high = 0.5 cutoff_low = 200 powerline = 60 order = 6 #print(signal) plt.figure(1) ax1 = plt.subplot(321) plt.plot(signal) ax1.set_title("Raw signal") conditioned_signal = final_filter(signal, fs, order) ax2 = plt.subplot(322) plt.plot(conditioned_signal) ax2.set_title("Conditioned signal") hsignal = highpass(signal, fs, order) ax3 = plt.subplot(323) plt.plot(hsignal) ax3.set_title("Only highpass filter") lsignal = lowpass(signal, fs, order) ax4 = plt.subplot(324) plt.plot(lsignal) ax4.set_title("Only lowpass filter") nonotch_1 = highpass(signal, fs, order) nonotch = lowpass(nonotch_1, fs, order) ax5 = plt.subplot(325) plt.plot(nonotch) ax5.set_title("High and low pass") onlynotch = notch(signal, powerline, 30) ax6 = plt.subplot(326) plt.plot(onlynotch) ax6.set_title("Notch filter only") plt.show() Continue reading...
