# FIR filter Interpolation vs Resampler

**URL:** <https://www.ruby-forum.com/t/fir-filter-interpolation-vs-resampler/232965>\
**Category:** GNU Radio\
**Created:** [November 7, 2014, 10:11am UTC](https://www.ruby-forum.com/t/fir-filter-interpolation-vs-resampler/232965 "2014-11-07T10:11:39Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [November 7, 2014, 10:11am UTC](https://www.ruby-forum.com/t/fir-filter-interpolation-vs-resampler/232965/1 "2014-11-07T10:11:39Z")

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Hi

I derive the output of a signal, both to an Interpolating FIR filter and  
Rational Resampler (in parallel) and then I connect them to a Time Sink  
(with 2 inputs).  
I use the same interpolation factor for both blocks (interpolation = 4).  
I also use in taps the same rcc filter.  
In Time Sink plot I observe a time delay in these 2 signals.  
Does anyone know why this happens?

Thank you  
Daniel

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**Author:** ![danielb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/c57346/32.png) [@danielb](https://www.ruby-forum.com/u/danielb)\
**Post date:** [November 7, 2014, 12:26pm UTC](https://www.ruby-forum.com/t/fir-filter-interpolation-vs-resampler/232965/2 "2014-11-07T12:26:31Z")

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Hi Daniel,

because both introduce delays and the delay of one of these is 2  
samples longer.

Greetings,  
Marcus

On 07.11.2014 10:07, Daniel B. wrote:

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**Author:** ![danielb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/c57346/32.png) [@danielb](https://www.ruby-forum.com/u/danielb)\
**Post date:** [November 10, 2014, 9:22am UTC](https://www.ruby-forum.com/t/fir-filter-interpolation-vs-resampler/232965/3 "2014-11-10T09:22:28Z")

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What is the exact meaning of the parameter mu?  
[http://gnuradio.org/doc/doxygen-3.6/classgr\_1\_1filter\_1\_1mmse\_\_fir\_\_interpolator\_\_ff.html](http://gnuradio.org/doc/doxygen-3.6/classgr_1_1filter_1_1mmse __fir__ interpolator__ff.html)  
I do not understand it :S

2014-11-07 12:25 GMT+01:00 Marcus Müller [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

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**Author:** ![danielb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/c57346/32.png) [@danielb](https://www.ruby-forum.com/u/danielb)\
**Post date:** [November 10, 2014, 12:28pm UTC](https://www.ruby-forum.com/t/fir-filter-interpolation-vs-resampler/232965/4 "2014-11-10T12:28:04Z")

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Hi Carlos,

this might get a little too theoretical to discuss it on the mailing  
list, thus I’d like to point you at the Readme [1] file referenced by  
the doxygen page, as I think it explains mu as fractional delay quite  
nicely.  
The readme also references the book where the idea of the MMSE  
interpolator will be explained in more detail.

Best regards,  
Marcus

[1]

> <https://github.com/gnuradio/gnuradio/blob/v3.6.5/gnuradio-core/src/gen_interpolator_taps/README>

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**Author:** ![danielb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/c57346/32.png) [@danielb](https://www.ruby-forum.com/u/danielb)\
**Post date:** [November 12, 2014, 8:52am UTC](https://www.ruby-forum.com/t/fir-filter-interpolation-vs-resampler/232965/5 "2014-11-12T08:52:18Z")

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Ok, thank you 😉

2014-11-10 12:26 GMT+01:00 Marcus Müller [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):