[SciPy-user] FIR Filters

Bob.Cowdery at CGI-Europe.com Bob.Cowdery at CGI-Europe.com
Wed Feb 25 13:19:25 CST 2004


I am trying to get a windowed FIR filter to use in fast convolution
filtering.
 
I have tried using :
signal.remez(2048,[300,3000],[1],Hz=44100)
to generate a 2048 tap filter, which is what I have used previously in Intel
IPP. Firstly, this gives me an array full of QNAN errors. Infact the only
time I don't get errors is by using a very small number of taps, say 10.
Various other values of taps fails to converge or gives QNAN errors. With
the 2048 taps it is also very, very slow (about 75 seconds on a 1.2GHz). The
IPP implementation is sub-second. I don't know if it's throwing an exception
on every QNAN or quite what is hapenning. 
 
I am also confused by not being able to specify a window type and I really
need lowpass not bandpass. I can see there is a function get_window() but I
don't know how this relates to an FIR filter when the only other parameter
is fftbins. Do I do something like tell it the number of fftbins I want the
filter to cover (I have 2048 bins of around 10Hz each) then shift it to the
correct part of the spectrum?
 
Any help appreciated.
 
Bob
 
 
Bob Cowdery
CGI Senior Technical Architect
+44(0)1438 791517
Mobile: +44(0)7771 532138
bob.cowdery at cgi-europe.com <mailto:bob.cowdery at cgi-europe.com> 
 
 
 

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