Your problem arises because one frequency value you ask for corresponds
exactly to a zero of hz.num
log(roots(hz.num))/(2*%pi)
so you want to compute the gain in dB of a zero value which is -inf
To avoid such problem you can let repfreq to do the frequency
discretization.
[frq,repf]=repfreq <repfreq.html>(hz)
or equivalently
[frq,repf]=repfreq <repfreq.html>(hz,0,0.5)
in this case the discretization uses varying frequency step
Serge
Le 23/02/2016 14:41, grivet a écrit :
Le 23/02/2016 14:21, Serge Steer a écrit :
Please can you give more details :
value of Order and Fcutoff/Fs/2
and what you are doing with hz (because iir does not call dbphi)
Serge
I am just running the example found in "how to design an elliptic
filter". Here is the code:
Order = 2; // The order of the filter
Fs = 1000; // The sampling frequency
Fcutoff = 40; // The cutoff frequency
// We design a low pass elliptic filter
hz = iir <iir.html>(Order,'lp','ellip',[Fcutoff/Fs/2 0],[0.1 0.1]);
// We compute the frequency response of the filter
[frq,repf]=repfreq <repfreq.html>(hz,0:0.001:0.5);
[db_repf, phi_repf] = dbphi <dbphi.html>(repf);
// And plot the bode like representation of the digital filter
subplot <subplot.html>(2,1,1);
plot2d <plot2d.html>(Fs*frq,db_repf);
xtitle <xtitle.html>('Obtained Frequency Response (Magnitude)');
subplot <subplot.html>(2,1,2);
plot2d <plot2d.html>(Fs*frq,phi_repf);
xtitle <xtitle.html>('Obtained Frequency Response (Phase in degree)');
with 'ellip' replaced by 'butt', and [Fcutoff/Fs/2 0] replaced
byFcutoff/Fs/2.
I am beginning to use digital filters to treat some data. As my first
step, I try to run the examples in the help,how to design an elliptic
filter (using Scilab 5.5.1, Win7-64). This works . However, when I
select a Butterworth filter:
hz = iir(Order,'lp','butt',Fcutoff/Fs/2,[0.1 0.1]);
I get this error message:
Singularité de la fonction log ou tan.
at line 6 of function dbphi called by :
[db_repf, phi_repf] = dbphi(repf);
What did I miss ?
No bugs have been reported for function dbphi, but three similar
bugs are listed for iir.
Any suggestion welcome.
JPGrivet
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