Re: [Discuss-gnuradio] resample ratio for fractional_resampler

[Andy Walls]

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.

-Andy