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Stefan Sydow st at metafly.infoHi Michael, > Thanks for the script, just some minor notes: SAMP_RATE should be > 28.8e6, not 28e6. Also you don't seem to do any overflow checking on the > conversion. If you are trying to build narrow filters, I expect you > might hit the 1/16 limit on the outer 8 coefficients, so the filter > coefficients might need to be shrunk (reducing the filter gain, of > course) before converting to integers. Good point. Thanks > I'm afraid that constructing a filter using gnuradio firdes and then > truncating it to 32 coefficients is likely not resulting in a good > filter. In my oppinion (not backed by math knowledge in that area, > though), the filter length should already be considered during > coefficient generation. Yes that's right. Using gnuradio firdes was a first hack with acceptable error as the fft shows. A better way is to use sinc() and a window function. Had a look into my "Signale and Systeme" script. There is also a software called winfilter if you want a 'classic' filter. It works well under wine. http://www.winfilter.20m.com/ > It looks like your plot uses the convention that 10dB is a factor of 10. > As the filter affects amplitude values and not power values, you should > use 20dB for a factor of 10, if I understand the dB scale correctly. I missed that too. A fix version is attached. Regards, Stefan -------------- next part -------------- A non-text attachment was scrubbed... Name: fir_coeff.py Type: text/x-python Size: 3417 bytes Desc: not available URL: <http://lists.osmocom.org/pipermail/osmocom-sdr/attachments/20120715/a65f9dfd/attachment.py>