[Discuss-gnuradio] Fractional resampling

[Martin Braun]

Hi,

having looked at the current codebase, I find two resamplers suitable
for interpolation rates close to 1: gr_fractional_interpolator and
gr_pfb_arb_resampler. I can see the latter is newer.
Here some questions:

1) When would I use which one, or is gr_fractional_interpolator
   simply older? I can tell they use different approaches (MMSE vs. linear
   interpolation), but don't really know what to do with this
   information :)

2) Concerning gr_fractional_interpolator: The first parameter, called
   phase_shift in the block definition and is later on referred to as
   'mu', seems to be an initial fractional delay. For an infinite
   stream, why does this matter? It seems to be important, otherwise it
   would not be the first argument of the block constructor (or is this
   coincidence? If it's pretty much irrelevant, why not make it second
   and then give it mu=0 as default value?)

3) Concerning gr_pfb_arb_resampler (I hope I've understood the code
   correctly): This uses a PFB to get the sampling rate close to what we
   want, and then linearly interpolates. Isn't this a bit inaccurate?
   I'm afraid I haven't got Harris' book right here, so I can't check
   the reference, but perhaps someone who's already used this resampler
   can share some experience?

Thanks a lot for any answers! They'll be greatly appreciated.

Cheers,
MB
-- 
Karlsruhe Institute of Technology (KIT)
Communications Engineering Lab (CEL)

Dipl.-Ing. Martin Braun
Research Associate

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Building 05.01
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Phone: +49 721 608-3790
Fax: +49 721 608-6071
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KIT -- University of the State of Baden-Württemberg and
National Laboratory of the Helmholtz Association

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