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[[Category:Block Docs]]
 
[[Category:Block Docs]]
This block implements a decimating filter using the fast convolution method via an FFTIt is an alternative to the [[Decimating FIR Filter]], useful when there is a large number of taps.
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[[Category:Stub Docs]]
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This is the template for the [[:Category:Block_Docs|"Page-per-block Docs"]].  This first section should describe what the block does and how to use it, using however many paragraphs necessary.  Note that the title of the wiki page should match the block's name in GRC, i.e. the one defined in the block's .grc fileLook at the [[FFT]] Block for a good example.
  
This filter is implemented by using the FFTW package to perform the required FFTs. An optional argument, nthreads, may be passed to the constructor (or set using the set_nthreads member function) to split the FFT among N number of threads. This can improve performance on very large FFTs (that is, if the number of taps used is very large) if you have enough threads/cores to support it.
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As this is a basic template, it's also in the [[:Category:Stub_Docs|"Stub Docs category"]]. Please improve it.
 
 
For standard filters such as lowpass, highpass, bandpass, etc., the filter.firdes and filter.optfir classes provide convenient generating methods.
 
  
 
== Parameters ==
 
== Parameters ==
 
(''R''): <span class="plainlinks">[https://wiki.gnuradio.org/index.php/GNURadioCompanion#Variable_Controls ''Run-time adjustable'']</span>
 
(''R''): <span class="plainlinks">[https://wiki.gnuradio.org/index.php/GNURadioCompanion#Variable_Controls ''Run-time adjustable'']</span>
  
; Decimation
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; Param 1 (''R'')
: Decimation rate.  The output stream will have this decimation applied to it.  A decimation rate of 1 simply means no decimationIf decimation is set higher than 1, make sure the filter will remove energy outside of the "output region", i.e. -Fs/2 to Fs/2 where Fs is the input sample rate divided by the decimation rate.
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: Description of parameter, provide any tips or recommended valuesNote that the name of the parameter above should match the param's label that shows up in grc (e.g. Sample Rate).
 
 
; Taps (''R'')
 
: Taps to use in FIR filter.
 
 
 
; Sample Delay
 
: Number of additional samples to delay signal by.
 
  
; Number of Threads
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; Param 2
: Number of threads to use for this block, i.e. to increase performance on multicore CPUs.
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: blah blah blah
  
 
== Example Flowgraph ==
 
== Example Flowgraph ==

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