Whenever you do an efficient implementation of the rational ratio resampler, you pick out one of the polyphase arms to do the actually evaluation of the filter taps and skip all of the implied zeros in the upsampled signal (for the obvious computational advantage). BUT, you can pick which "phase" or step to start evaluating the filter. This is the genesis of the term "polyphase".
HOWEVER, the fractional interpolator is NOT the rational resampler which is http://gnuradio.org/trac/browser/gnuradio/trunk/gnuradio-core/src/lib/filter /gr_rational_resampler_base_XXX.cc.t and the fractional interpolator is intended for use with resampling ratios that would require HUGE filters to be partitioned in order to achieve the rational resampler. Since all digital computers are by their nature, rational number machines, it would be possible, but onerous. Bob ARRL SDR Working Group Chair Member: ARRL, AMSAT, AMSAT-DL, TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. "Trample the slow .... Hurdle the dead" -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Brian Padalino Sent: Tuesday, October 21, 2008 10:34 AM To: Clark Pope Cc: discuss-gnuradio@gnu.org Subject: Re: [Discuss-gnuradio] fractional_interpolator_cc? On Tue, Oct 21, 2008 at 10:15 AM, Clark Pope <[EMAIL PROTECTED]> wrote: > > I'm not able to get this function to work correctly. I have it just connected between a snapshot file and an output file. I set the interpolation factor to 2.0 and the output file ends up half the size of the input file. It's like it is a decimation block instead of interpolation? How does the rational resampler work out - or can you not represent the ratio as a rational number? Are you calling it correctly? It seems as if there is a phase shift as well as an interpolation ratio being passed in. http://gnuradio.org/trac/browser/gnuradio/trunk/gnuradio-core/src/lib/filter /gr_fractional_interpolator_cc.cc#L38 http://gnuradio.org/trac/browser/gnuradio/trunk/gnuradio-core/src/lib/filter /gr_fractional_interpolator_cc.cc#L67 There may be an issue here: http://gnuradio.org/trac/browser/gnuradio/trunk/gnuradio-core/src/lib/filter /gr_fractional_interpolator_cc.cc#L49 Might be upside down? Brian _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
