Re: [Discuss-gnuradio] Proper setting for sample delay for polyphase arbitrary resampler?

On Tue, Jun 24, 2014 at 2:15 PM, Andy Walls <andy@silverblocksystems.net> wrote:

Hi,

I have a Polyphase Arbitrary Resampler block in a flow graph and I want
to set the "Sample Delay" parameter so GnuRadio delays tags properly.

With the following parameters:

   Input Sample Rate: Fs
   Resampling Rate:   r = output_rate / Fs
   Number of Filters: N
   Taps:              taps=firdes.low_pass_2(N, N*Fs, ..., ..., ...,)

The best I can figure is to set:

   Sample Delay:      int(round((math.ceil(len(taps)/N) - 1.0)/2.0))

because GnuRadio applies this "Sample Delay" as offset to the tags
before scaling the tag offsets by the resampling rate r.

Can anyone confirm this is correct, or is there something I'm missing?

Thank you.

Regards,
Andy

Andy,

Take a look at pfb_arb_resampler.cc. In the constructor, it calculates the sample delay. It's close to what you're thinking, but scaled for the polyphase filterbank partitioning.

Tom