Displaying epoched signal

About the GUI application to design signal processing pipelines
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ariandy
Posts: 25
Joined: Fri Aug 14, 2009 3:11 am

Displaying epoched signal

Post by ariandy »

Dear OpenViBE developers,

I'm sorry if this is a stupid question, is it possible to display epoched signal? If its possible, where exactly I can tap input for Signal Display Box?

I'm learning how randomly-looked EEG signal transforms step by step until it can be recognised (feature extracted), from the motor-imagery sample scenario. But I'm stuck after the signal exits from epoching box.

And also, what does log(1+x) do after signal's power calculated? I've managed to get this screenshot after bypassing continuous signal to the DSP box:
Image
I must confess I'm not really good with mathematics of signal processing, but from the screenshot I don't understand what is the purpose of the logarithm. Visually, signal power is more recognizable than logarithm one.

Please pardon my stupidness.

Thank you :)
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lbonnet
Site Admin
Posts: 417
Joined: Wed Oct 07, 2009 12:11 pm

Re: Displaying epoched signal

Post by lbonnet »

Hi ariandy !
is it possible to display epoched signal?
Yes it is. Link a Signal Display after the Time Based Epoching, play the scenario and change the configuration of the signal display panel. If you want to see every epoch, use a time scale equals to the epoch duration (1 sec in this scenario). Please change this time scale after playing the scenario (there is a bug we need to fix when the time-scale has been previously set). You will see Every epoch computed (i.e. every intervals).
And also, what does log(1+x) do after signal's power calculated? [...] Visually, signal power is more recognizable than logarithm one.
I am not a specialist of signal processing and mathematical operations, but I can try to explain what I know :)
In fact, we don't want to detect the signal peaks, but power peaks on a given frequency band - not visible on the signal display.
The log(1+x) gives a logarithmic distribution of the power, to get close to a normal distribution.

I hope this helps, but if an openviber with better knowledge of signal processing theory can precise it, (s)he's welcomed ;)

Laurent-
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Checkout my (old) blog for some OpenViBE tips & tricks : here !

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