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Re: [Discuss-gnuradio] atsc_cpll finally works
From: |
Eric Blossom |
Subject: |
Re: [Discuss-gnuradio] atsc_cpll finally works |
Date: |
Fri, 23 May 2008 11:07:50 -0700 |
User-agent: |
Mutt/1.5.17 (2007-11-01) |
On Fri, May 23, 2008 at 09:00:31AM -0400, Achilleas Anastasopoulos wrote:
> OK, I see.
>
> 1) Usually in fractional interpolators the trade-off is: more taps vs finer
> sampling. It might be possible to increase the number of taps and still be
> able to work with only a 12.8 (or 16) real-Msps.
> Having said that, I have to admit I haven't looked at exactly what this
> particular timing loop is doing.
The current resampler requires only 8 taps at each possible fractional
point (1/128). It manages this by having a frequency response that is
unconstrained between Fs/4 and Fs/2. That's the source of the
constraint on sample rate and occupied bandwidth. The filter design
code is in gnuradio-core/src/gen_interpolator_taps. See the README
there for additional info and references.
We could use a different fractional interpolator, perhaps the one by
Julius O. Smith: http://ccrma-www.stanford.edu/~jos/resample.
With it, 12.8 real-MS/s or 16 real-MS/s should be possible.
Eric