I will submit the patch. regarding the sign change in frequency, I didn't mean to change the convention: the sign change IS REQUIRED in order to KEEP the convention because now the taps are not reversed...
Achilleas On Wed, Oct 9, 2013 at 9:20 AM, Tom Rondeau <t...@trondeau.com> wrote: > On Tue, Oct 8, 2013 at 9:39 PM, Achilleas Anastasopoulos > <anas...@umich.edu> wrote: > > > > I was playing around with > > > > fir_filter_XXX > > > > and > > > > freq_xlating_fir_filter_XXX > > > > and noticed that the two do not give the same output > > for the same input (and center_freq=0 in the xlating filter). > > > > Looking at the implementation of the latter > > it is obvious why: the taps are reversed in the line: > > > > std::reverse(ctaps.begin(), ctaps.end()); > > > > For consistency the taps should not be reversed (as in all other filters) > > We also need to set > > Yes, please submit a patch for this. The taps are reversed inside the > fir filters, so this is redundant and confusing. Most people probably > use symmetric filter taps, which is why it has not been found. > > > float fwT0 = 2 * M_PI * d_center_freq / d_sampling_freq; > > > > (instead of the minus sign in the code). > > > > unless there is an objection, I will go ahead and push a correction, > > Achilleas > > Don't change the sign of the frequency. I know this is controversial, > but from my experience with users, more people find the current way > easier to understand. We're telling the filter what the center > frequency is, which means that we will take a signal at Fc and > downshift it to DC. To me, if we're on carrier Fc and we specify -Fc > as the "Center Frequency", that's more confusing. > > Tom >
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