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 Post subject: how FFT box work
PostPosted: Mon Jun 15, 2015 11:51 am 
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Joined: Sun Nov 23, 2014 5:32 am
Posts: 21
If I have 14 channels, how FFT box will compute the spectrum? does it concatenate the 14 channel together ,which is give a single channel with a length of 14 times the length of EEG channel? if yes, how much is that correct? what is the problem of calculate the spectrum for each channel, which is in my opinion is more convenience ?

Thanks in advance.


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 Post subject: Re: how FFT box work
PostPosted: Tue Jun 16, 2015 2:39 pm 
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Joined: Tue Dec 04, 2012 3:53 pm
Posts: 599
Location: INRIA Rennes, FRANCE
Hi, if you look at the bundled power-spectrum.xml tutorial, you'll see the power of each channel appears separately.


Cheers,
Jussi


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 Post subject: Re: how FFT box work
PostPosted: Tue Jun 16, 2015 4:19 pm 
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Joined: Sun Nov 23, 2014 5:32 am
Posts: 21
I have forward the output of "fft" box to "signal display" box, which is show it as a single channel.

So what is the size of the matrix that came out from the amplitude pin, for example ,number of channels X number of frequencies sample ?


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 Post subject: Re: how FFT box work
PostPosted: Wed Jun 17, 2015 8:02 am 
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Joined: Tue Dec 04, 2012 3:53 pm
Posts: 599
Location: INRIA Rennes, FRANCE
HA3 wrote:
I have forward the output of "fft" box to "signal display" box, which is show it as a single channel.

The output of the FFT box is a spectrum, a stream type that signal display doesn't support. Instead, it interprets it as a matrix. In 1.0.1 you should be able to send at least the amplitude output to signal display and see it as separate channels (although it looks a bit funny). Try adding the signal display box to the tutorial scenario I mentioned.

HA3 wrote:
So what is the size of the matrix that came out from the amplitude pin, for example ,number of channels X number of frequencies sample ?


You can use the EBML stream spy box to find this out (and whatever else that is going on in each stream).


Cheers,
Jussi


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 Post subject: Re: how FFT box work
PostPosted: Wed Jun 17, 2015 8:25 am 
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Joined: Tue Dec 04, 2012 3:53 pm
Posts: 599
Location: INRIA Rennes, FRANCE
Btw, the stream contents are also described here with a bit more verbosity,

http://openvibe.inria.fr/stream-structures/


Jussi


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