[SciPy-user] butterworth filter

Stef Mientki s.mientki@ru...
Tue Sep 16 12:25:58 CDT 2008



cyril giraudon wrote:
> I didn't understand abscissa differences.
> in fact, x (normalized frequency) are devided by pi.
>
> However, in low frequency, scipy trunsfer function is very low.
> At 0.2, scipy : -250dB, matlab : -120dB.
As an engineer I would say -120 dB equals -250 dB, so the graphs are equal.
I really would like to see your lab, if your interested -250 dB ;-)
In Matlab you probably never get to know how the frequency response is 
calculated,
although presumable it's just a copy of  "Numerical recipes".
At  -120 dB, the rounding results might become relevant.
It would be interesting to compare the calculated filter coefficients,
or the zero/pole values,
and maybe even put the Matlab coefficients into Scipy and vise versa.

cheers,
Stef


>
> Is there any explanation ?
>
> Thanks a lot,
>
> Cyril.
>
>
>
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