No problem! Like Marcus says I definitely have to think hard about the implementation and benchmark... But it's an interesting special case. Would be neat with a special block for it that also calculates the coefficients.
--Albin On Wed, Apr 24, 2019, 10:39 Derek Kozel <de...@bitstovolts.com> wrote: > Oops, accidentally went direct rather than through the list. > > It would be a good addition to gr-filter to be able to use the CPU > operations optimized halfband out of the box. > > ==== Previous message ==== > Hi Albin, > > The Filter Design Tool will generate Halfband taps that can be loaded into > the FIR filter block, no need to write one. > > The implementation is here: > > https://github.com/gnuradio/gnuradio/blob/master/gr-filter/python/filter/design/fir_design.py#L161 > > What would be an excellent addition would be to move the implementation > for half-band creation to the firdes class and then have the filter design > tool call the function, as it does for most (all?) of the other filter > classes. > > https://github.com/gnuradio/gnuradio/blob/master/gr-filter/include/gnuradio/filter/firdes.h#L60 > > Regards, > Derek > ==== > > On 24/04/2019 09:04, Müller, Marcus (CEL) wrote: > > Hi Albin, > > Don't know what Derek suggested, but be aware that our "straight" FIR > filter decimators are already polyphase implementations, and use SIMD > (through VOLK) heavily (run volk_profile if you want to make maximum > use of that advantage); it might be that on paper, the number of > operations are unnecessarily high, but in CPU practice, some cures are > worse than the disease. > > For example, I haven't tried, but it's thoroughly possible that albeit > the classical case of "half your tap memory by only storing one half of > your symmetrical FIR" performs worse than just working with the full > (half redundant) tap vector, simply because doing so avoids nonlinear > memory access patterns. > > Best regards, > Marcus > > On Tue, 2019-04-23 at 19:06 +0200, Albin Stigö wrote: > > Thanks for the reply Marcus. Interesting approach for sure! Will have to > think about it... > > Derek, your solution works but it will be 4 times slower than the example I > linked to. > > > --Albin > > > On Tue, Apr 23, 2019, 18:24 Müller, Marcus (CEL) <muel...@kit.edu> > <muel...@kit.edu> wrote: > > Hi Albin, > > I'm very very tired right now, but me and Felix came to the following > conclusions on our *Whiteboard Of Wisdom, Smarts, Expertise, > Rationality and Science* (WOWSERS): > > 1. A Nyquist-M bandpass filter, esp. a halfband, has zeros on every > other tap – except for the one center tap, which is at the maximum of > the sinc that you window your prototype filter with. > 2. you'd thus implement that filter as polyphase filter with two > different polyphase components: > 1. one polyphase component that contains all the zeros, and the > single center tap that's not > 2. one component that contains all the non-zero taps > 3. you'd thus need to "deinterleave" your input stream into two: > 1. Delay by half the number of taps (and multiply by the maximum > 2. filter with all the non-zero taps > 4. sum up the results > > So, for all this, we already have blocks – yay! > > Best regards, > Marcus > > On Tue, 2019-04-23 at 17:45 +0200, Albin Stigö wrote: > > Just checking before I write one, is there a half band decimator/interpolator > in gnuradio I haven't been able to find... > > Optimized like this:http://liquidsdr.org/doc/resamp2/ > > Or is there an even better option for interpolation by 2? > > > --Albin > _______________________________________________ > Discuss-gnuradio mailing > listDiscuss-gnuradio@gnu.orghttps://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > _______________________________________________ > Discuss-gnuradio mailing > listDiscuss-gnuradio@gnu.orghttps://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >
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