[FieldTrip] Emotiv and Fieldtrip - filter in the streamer/buffer?

Ricardo Jorge landpt at gmail.com
Wed Sep 26 20:53:05 CEST 2012

Hello there once again,

I've contacted you some days ago because I was having troubles reading
the data from the Emotiv in the Fieldtrip toolbox, which you replied
and solved my trouble. Thanks once again.

However, being worked on the data, I've noticed something odd that I
cannot understand what exactly is happening:
- I did not activate or put any filter (even removed the preprocessing
baseline command) and  the signals that I get in the fieldtrip have
around 4000-5000 of mean and the variance is almost 0.05, something
like that.
- At the same time, I was running Emotiv Testbench and for some weird
reason, the signals that I get in there have exactly the same mean,
but its variance is more than 1 (something like between 1 and 1.5).
- At the same time, I did run OpenVibe, which was similar to the Testbench.

Seeing their plots, there are clearly some variations:
Testbench/Openvibe gave much more "peaks" and spread, whereas
Fieldtrip (streamer) looks less noisy, as if it was almost-perfect.
But I did not apply any filter...

Can I have any information about what could be happening here? Does
the streamer/buffer apply some filter that I don't know? I've seen
that it is not possible to acquire raw data from Emotiv, except using
Emotiv SDK, Openvibe or Emokit. Is it related?

Thanks in advance.

Ricardo Jorge

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