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

Boris Reuderink b.reuderink at donders.ru.nl
Thu Sep 27 11:24:34 CEST 2012

Dear Ricardo,

If I understand your remark correctly, there is a scaling difference between other software (OpenVibe & Emotiv Testbench) and FieldTrip's real-time signal from the Emotiv. Would could see if we can find this difference in scaling. 

But, are there other signal characteristics that are different? You mention 'less noisy' — could that be caused just by scaling, or do you have a clear indication that the signal is filtered? Screenshots would be helpful.

There are some places were filtering could take place. The viewer (bufferViewer.exe) has an option to enable a high-pass filter, and the FieldTrip's shared ODM code for streaming can down-sample the signal which also involves filtering, but it should be disabled by default.

Can you provide some additional info?



PS: emotiv2ft.exe is based on the Emotiv SDK (EDK).

twitter.com/#!/breuderink | github.com/breuderink | borisreuderink.nl

On 26 sep. 2012, at 20:53, Ricardo Jorge <landpt at gmail.com> wrote:

> 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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