FIR and IIR filter examples in SciPy (from http://mpastell.com/)

Import signal processing library: %CODE{lang="python"}% from pylab import * import scipy.signal as signal %ENDCODE%

FIR Filters

Lowpass

%CODE{lang="python"}% n = 61 a = signal.firwin(n, cutoff = 0.3, window = "hamming") #Frequency and phase response mfreqz(a) show() #Impulse and step response figure(2) impz(a) show() %ENDCODE%

Functions for frequency, phase, impulse and step response %CODE{lang="python"}% #Plot frequency and phase response def mfreqz(b,a=1): w,h = signal.freqz(b,a) h_dB = 20 * log10 (abs(h)) subplot(211) plot(w/max(w),h_dB) ylim(-150, 5) ylabel('Magnitude (db)') xlabel(r'Normalized Frequency (x$\pi$rad/sample)') title(r'Frequency response') subplot(212) h_Phase = unwrap(arctan2(imag(h),real(h))) plot(w/max(w),h_Phase) ylabel('Phase (radians)') xlabel(r'Normalized Frequency (x$\pi$rad/sample)') title(r'Phase response') subplots_adjust(hspace=0.5)

#Plot step and impulse response def impz(b,a=1): l = len(b) impulse = repeat(0.,l); impulse[0] =1. x = arange(0,l) response = signal.lfilter(b,a,impulse) subplot(211) stem(x, response) ylabel('Amplitude') xlabel(r'n (samples)') title(r'Impulse response') subplot(212) step = cumsum(response) stem(x, step) ylabel('Amplitude') xlabel(r'n (samples)') title(r'Step response') subplots_adjust(hspace=0.5) %ENDCODE%

IIR Filters:

%CODE{lang="python"}% b,a = signal.iirdesign(wp = [0.05, 0.3], ws= [0.02, 0.35], gstop= 60, gpass=1, ftype='ellip') mfreqz(b, a) impz(b, a) %ENDCODE%

Code from: http://mpastell.com/2010/01/18/fir-with-scipy/

scipy.signal documentation

-- MikeHadmack - 03 Sep 2010