newbie question : how to combine channels within a signal

[asparagus]

Hi all,

I have a simple problem: I have a 32-channel EEG signal, and I would like to calculate the amount of alpha activity averaged over all channels, so that I have input signal of 32 channels, and output signal of one channel with the average of all 32 channels.

Similarly, what if I want to calculate the ratio of Beta vs. Alpha activity? How do I access different channels in a signal. I tried simple dsp by giving it signal with two channels, and had a calculation of a+b, expecting the sum of two channels as one channel signal, but I received again two channel signal.

kind regards

[fabien.lotte]

Hi Asparagus!

If you want to combine different channels, for instance to do averaging, the best box to use is the spatial filter box, which creates a linear combination of channels:

http://openvibe.inria.fr/documentation/ ... ilter.html

I hope this helps,

Fabien

[jtlindgren]

Agree with Fabien. And about the way Simple DSP works: you can use formulas across streams (e.g. a+b is a pairwise sum of the matrix chunks of streams a and b), but it cannot be utilized to do math on a channel vs channel level. If you really need to do that, you can use two channel selectors to split the stream, then give the two streams to simple dsp as a and b.


Cheers,
Jussi