This is not the first time this has come up, and yes, patches are welcome. The simplest fix might be to add a factory-time argument that disables the resampler entirely -- this will guarantee no sample offsets, ever, but of course will not allow to change the timing offset at runtime.
M On 06/28/2016 07:47 PM, Raj Bhattacharjea wrote: > Thanks for the hints for where to look and why this happens from a code > perspective. I don't think it makes sense from a semantic perspective > (if the user says taps=1, she should get the unity gain delay free > channel) but I'm guessing "patches are welcome" is the appropriate > response to this minor usability issue. > > On Tuesday, June 28, 2016, Andrej Rode <m...@andrejro.de > <mailto:m...@andrejro.de>> wrote: > > Hey Raj, > > > introduces a delay that can be corrected by applying the taps > [0,0,0,1]. > > See the attached flowgraph that subtracts the signals before and after > > the channel model; if you let taps = 1, the two signals don't > cancel. If > > you use taps = [0,0,0,1], they do. > > The delay you are seeing is introduced by the fractional_resapmler > inside the channel_model block. The FIR filter inside the fractional > resampler needs to build up and therefore introduces a initial delay of > three samples. > > If you want to know more about the insides of the channel model I > suggest you look at the sources [0][1] yourself. > > Greetings, > Andrej > > [0] ./gr-channels/lib/channel_model_impl.cc > [1] ./gr-channels/lib/channel_model_impl.h > > > > -- > Raj Bhattacharjea, PhD > Georgia Tech Research Institute > Information and Communications Laboratory > http://www.prism.gatech.edu/~rb288/ <http://www.prism.gatech.edu/~rb288/> > 404.407.6622 > > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio