# What does noutput mean in a FFT block whic fft\_len=2048?

**URL:** <https://www.ruby-forum.com/t/what-does-noutput-mean-in-a-fft-block-whic-fft-len-2048/239669>\
**Category:** GNU Radio\
**Created:** [March 10, 2014, 3:58am UTC](https://www.ruby-forum.com/t/what-does-noutput-mean-in-a-fft-block-whic-fft-len-2048/239669 "2014-03-10T03:58:42Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![musicdenotation](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ea666f/32.png) [@musicdenotation](https://www.ruby-forum.com/u/musicdenotation)\
**Post date:** [March 10, 2014, 3:58am UTC](https://www.ruby-forum.com/t/what-does-noutput-mean-in-a-fft-block-whic-fft-len-2048/239669/1 "2014-03-10T03:58:42Z")

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hi,  
i want deal the data after FFT in my own block,i copy a  
fft\_len_sizeof(gr\_complex) length of data from in to a buffer,then deal  
the data ,and copy the dealed data from buffer to the out,  
in a FFT blocks,if there is  
size\_t block\_size=output\_signature()-\>sizeof\_stream\_item(0);  
when i use memcpy(out,in,block\_size_noutput ); it works normally ,  
but when i do it like this :memcpy(out,in, fft\_len\*sizeof(gr\_complex)  
);,it does not work

does the result of block\_size_noutput have any relations with  
fft\_len_sizeof(gr\_complex)  
or some other suggestions  
thanks,  
BZS

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**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\
**Post date:** [March 10, 2014, 9:04am UTC](https://www.ruby-forum.com/t/what-does-noutput-mean-in-a-fft-block-whic-fft-len-2048/239669/2 "2014-03-10T09:04:41Z")

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Hi BZS,  
you’re mixing concepts here: the FFT len is your FFT size, but noutput  
is the number of items you are allowed to produce (maximum).  
Please re-read the writing an out-of-tree module wiki page to  
understand the difference better 🙂

Greetings,  
Marcus

On 10.03.2014 03:21, ??? wrote:

> does the result of block\_size_noutput have any relations with  
> fft\_len_sizeof(gr\_complex) or some other suggestions thanks, BZS
> 
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