On Sat, Aug 27, 2005 at 06:08:34AM +0100, kelvin loi wrote: > Hi all, > Has anybody out there dive into the C++ code for the > gr.fir_filter_xxx() block??? Because i just wondering > why GNU radio can actually do decimation before the > polyphase FIR filter? That actually is not allowed in > signal processing theory isn't it? Because it will > cause aliasing. Please give me some guidance. Thanks. > > Cheers, > kelvin
gr.fir_filter_xxx does not use a polyphase implementation. It's a normal "dot product" implementation with O(n*m) runtime where n is the number of taps and m is the number of input samples. However, the constant is *very* small, typically 1 on x86 machines. We ought to be able to get to 0.5 on AMD64 (2 FADDs and 2 FMULTs / cycle). For filters with more than about 16 taps, gr.fft_filter_xxx is faster, though it depends on the decimation factor. YMMV. Eric _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
