[SciPy-user] butterworth filter
cyril giraudon
cyril.giraudon at free.fr
Tue Sep 9 09:37:26 EDT 2008
Hi,
I use scipy 0.6.0 and i try to reproduce the plot of the matlab butter
function web documentation (first response for a google request "matlab
butter example").
The matlab code is :
[z,p,k] = butter(9,300/500,'high');
[sos,g] = zp2sos(z,p,k); % Convert to SOS form
Hd = dfilt.df2tsos(sos,g); % Create a dfilt object
h = fvtool(Hd); % Plot magnitude response
set(h,'Analysis','freq') % Display frequency response
In scipy, I write :
from scipy.signal import butter, freqz
from pylab import show, grid, log, plot
b, a = butter(9, 300./500., 'high')
fi = freqz(b, a)
plot(fi[0], 20*log(abs(fi[1])))
grid()
show()
Why are the two filters not the same ?
Thanks a lot,
Cyril.
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