# Number of taps in pfb filter?

**URL:** <https://www.ruby-forum.com/t/number-of-taps-in-pfb-filter/231045>\
**Category:** GNU Radio\
**Created:** [July 18, 2014, 6:56am UTC](https://www.ruby-forum.com/t/number-of-taps-in-pfb-filter/231045 "2014-07-18T06:56:28Z")\
**Posts on this page:** 3\
**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:** [July 18, 2014, 6:56am UTC](https://www.ruby-forum.com/t/number-of-taps-in-pfb-filter/231045/1 "2014-07-18T06:56:28Z")

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hello list,  
when I am trying to channelize a baseband with following specs:  
sample rate: 2MHz  
bandwidth for low pass filter: 145kHz  
transition bandwidth: 10 kHz  
number of channels: 10  
pfb decimation: 4

When I see number of channels is 91 taps/channel, but I think its too  
much,  
please guide me how to reduce taps/channel

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**Author:** ![gsmandvoip](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/e19adc/32.png) [@gsmandvoip](https://www.ruby-forum.com/u/gsmandvoip)\
**Post date:** [July 18, 2014, 10:49am UTC](https://www.ruby-forum.com/t/number-of-taps-in-pfb-filter/231045/2 "2014-07-18T10:49:00Z")

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On 07/18/2014 06:55 AM, gsmandvoip wrote:

> hello list,  
> when I am trying to channelize a baseband with following specs:  
> sample rate: 2MHz  
> bandwidth for low pass filter: 145kHz  
> transition bandwidth: 10 kHz  
> number of channels: 10  
> pfb decimation: 4
> 
> When I see number of channels is 91 taps/channel, but I think its too  
> much, please guide me how to reduce taps/channel

In order to reduce taps, you must increase the transition bandwidth. Use  
the filter design tool to get a feeling for this.  
Note that this is basic signal processing knowledge, if these things are  
unclear I recommend you study a DSP textbook. For recommendations, see  
the [gnuradio.org](http://gnuradio.org) wiki and the ‘suggested reading’ section.

Martin

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<div class="post-metadata">

**Author:** ![gsmandvoip](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/e19adc/32.png) [@gsmandvoip](https://www.ruby-forum.com/u/gsmandvoip)\
**Post date:** [July 18, 2014, 4:52pm UTC](https://www.ruby-forum.com/t/number-of-taps-in-pfb-filter/231045/3 "2014-07-18T16:52:18Z")

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On Fri, Jul 18, 2014 at 4:47 AM, Martin B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> > much, please guide me how to reduce taps/channel
> 
> In order to reduce taps, you must increase the transition bandwidth. Use  
> the filter design tool to get a feeling for this.  
> Note that this is basic signal processing knowledge, if these things are  
> unclear I recommend you study a DSP textbook. For recommendations, see  
> the [gnuradio.org](http://gnuradio.org) wiki and the ‘suggested reading’ section.
> 
> Martin

I’d recommend fred harris’ book Multirate Signal Processing specifically  
to  
help you with this question.

Tom