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Re: [Discuss-gnuradio] resample ratio for fractional_resampler
From: |
Andy Walls |
Subject: |
Re: [Discuss-gnuradio] resample ratio for fractional_resampler |
Date: |
Tue, 24 Oct 2017 08:22:05 -0400 |
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