[SciPy-user] butterworth filter

Stef Mientki s.mientki@ru...
Wed Sep 17 02:59:26 CDT 2008


thanks David,

for correcting me.
Sorry, I think I generalized a problem I once had with Matlab too much.
But anyway such a statement reveals some of the essential details ;-)

cheers,
Stef

David Cournapeau wrote:
> Stef Mientki wrote:
>   
>> 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,
>>     
>
> That's not entirely accurate. A lot of matlab functions are implemented
> in matlab itself. That's the case for butterworth AFAICS (butterworth is
> a big .m file, suggesting the implementation itself is in matlab). I
> avoid reading the actual code itself, though, for licensing issues,
> because I work a lot on scipy/numpy. But if you don't intend to write
> this code for numpy/scipy, I guess you can read it.
>
>   
>> although presumable it's just a copy of  "Numerical recipes".
>>     
>
> IIRC, there is no signal processing code in Numerical recipes. For
> Butterworth, it should not be too difficult to check, though, because it
> is a direct implementation of the analog domain filters. That's
> certainly one of the easiest IIR to implement for anyone familiar with
> digital signal processing (bilinear transform and co to go into digital
> domain).
>
> Looking at the code, for butterworth, I think the scipy implementation
> may be a bit too naive in some corner cases. IIRC, you would be better
> implementing a N order filter by cascading 2n order filters. In a former
> life, I was really into synthesizer and digital sound processing, and I
> know that it mattered in fixed point and even floating point (32 bits)
> implementations, because for synthesizer, you like the corner cases (to
> make boom boom and make you ear bleed in clubs).
>
> cheers,
>
> David
> _______________________________________________
> SciPy-user mailing list
> SciPy-user@scipy.org
> http://projects.scipy.org/mailman/listinfo/scipy-user
>
>
>   


Het UMC St Radboud staat geregistreerd bij de Kamer van Koophandel in het handelsregister onder nummer 41055629.
The Radboud University Nijmegen Medical Centre is listed in the Commercial Register of the Chamber of Commerce under file number 41055629.




More information about the SciPy-user mailing list