Re: [Discuss-gnuradio] resample ratio for fractional_resampler

[Andy Walls]

On Tue, 2017-10-24 at 08:16 -0400, Andy Walls wrote:
> Hi Marcus:
> 
> Nice insights and plots.
> 
> > From:       Marcus Müller
> > Date:       Mon, 23 Oct 2017 20:10:23 +0200
> 
> [snip]
> > From the above figure, I'd say: go for 256 taps; 50 dB of anti-
> > aliasing should probably suffice.
> > On my machine, the 256 tap FIR filter with decimation=64 ran about
> > 20% faster than the fractional resampler; comparing what they do to
> > white noise, I'd say that whilst the spectral shape of the 256 tap
> > FIR is not perfect, the MMSE is pretty much unusable, I guess:
> 
> I'd just like to interject here that GNURadio's MMSE filterbank is
> only
> MMSE for input spectral components in the range [-sample_rate/4,
> sample_rate/4].
> 
> Also it appears that the mmse/fractional_resampler blocks don't
> perform
> any explicit anti-alias filtering.  So that's another reason to have
> a
> band-limiting filter out in front of it.

Oopsie, and maybe one after it too, since we're talking about
decimation.

-Andy