# Missing internal callbacks

**URL:** <https://www.ruby-forum.com/t/missing-internal-callbacks/230776>\
**Category:** GNU Radio\
**Created:** [July 3, 2014, 11:41pm UTC](https://www.ruby-forum.com/t/missing-internal-callbacks/230776 "2014-07-03T23:41:58Z")\
**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 3, 2014, 11:41pm UTC](https://www.ruby-forum.com/t/missing-internal-callbacks/230776/1 "2014-07-03T23:41:58Z")

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Hello-

when creating a flowgraph in GRC there are times I would like to change  
the decimation on-the-fly with a gui slider. However, this does not  
work because the decimation factor in blocks such as the AM Demod or  
Decimating Fir Filter does not have an internal callback (as I  
understand it). My main purpose is to be able to dynamically change the  
sampling rate to re-scale the x-axis in a gui fft sink while the  
flowgraph is operating. Is there a way around this? Is this a  
necessary limitation, or just something nobody has gotten around to  
implementing?

Thanks!

Eric

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**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [July 4, 2014, 4:38am UTC](https://www.ruby-forum.com/t/missing-internal-callbacks/230776/2 "2014-07-04T04:38:19Z")

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On Fri, Jul 4, 2014 at 5:40 AM, [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> 

It is not impossible to have a block that its decimation factor or/and  
sampling rate could be changed on the fly.  
Create your own block, inherited from general block.  
But it is tricky to code it correctly, need a lot of skill and testings.

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**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [July 4, 2014, 5:52am UTC](https://www.ruby-forum.com/t/missing-internal-callbacks/230776/3 "2014-07-04T05:52:51Z")

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It is a very difficult thing to implement practically and is so close to  
necessary limitation that you should just consider it necessary and move  
on.

Bob