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From: | Iain Young, G7III |
Subject: | Re: [Discuss-gnuradio] Xlate FIR filter broken in gr 3.7 |
Date: | Thu, 08 Aug 2013 21:37:03 +0100 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130623 Thunderbird/17.0.7 |
On 08/08/13 21:14, Johnathan Corgan wrote:
On 08/08/2013 01:01 PM, Andrew Davis wrote:It's not just you, I noticed this too. This change broke gr-atsc ( but I fixed that ). The problem is on line 80 of gr-filter/lib/freq_xlating_fir_filter_XXX_impl.cc.t: the 2 was not negative in 3.6 but is now, i'm not sure why.Good catch, thanks. The "old style" version of the block in gnuradio-core in 3.6.5.1 works correctly. The "new style" version of the block in gr-filter in 3.6.5.1 has the sign change. When all the old-style blocks were removed for 3.7, this of course left only the changed one. Since it was Tom who did the conversion on that block, I'll wait until he chimes in on whether his change was an accident or intentional.
I'll defer to those who know the code better than I, however I will note that the fact that it was "reverse" (ie negative values went "up" in frequency within the filter" confused me at first... ...But then I spoke to others that used other SDRs, and found that they had the same behaviour. So I stuck a sign in front, and carried on, believing it was some strange function of the way things worked deep in SDR theory, and didn't worry about it any more. Would suggest that if others do it this way (ie negative values in the FIR filter go up), it may be worth to keep that behaviour for convention's sake if there's no better reason to change it Best Regards Iain
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