order =5
fs = 500.0
cutoff =0.5
nyq = 0.5 * fs
normal_cutoff = cutoff / nyq
b, a = signal.butter(order,normal_cutoff,btype='high',analog=False)

plt.figure()


w, h = freqz(b, a, worN=8000)
plt.subplot(2, 1, 1)
plt.plot(0.5*fs*w/np.pi, np.abs(h), 'b')
plt.plot(cutoff, 0.5*np.sqrt(2), 'ko')
plt.axvline(cutoff, color='k')
plt.xlim(0,20)
plt.ylabel('Amplitude [dB]')
plt.title("Highpass Filter Frequency Response")
plt.xlabel('Frequency [Hz]')