[Eeglablist] .bdf data converted to microvolts

[Bradley Voytek]

Abigail:

The BioSemi data have such high values, because BioSemi uses some of
its bit depth to record the DC offsets, so the data are oscillating
around (in your case) 9000-1000 uV, instead of around 0. When you
apply a high-pass filter, you are by the very nature of the filter
removing this DC shift (0 Hz), which pulls the data into the
"expected" range.

There are a few other caveats to working with your BioSemi data, and
we've had these discussions on this list before, if you look through
the archives.

Good luck!

::brad

On Thu, Sep 11, 2008 at 10:28 AM, Abigail Mani <amani at uh.edu> wrote:
> EEGLAB users,
>
> EEG.data is in uV?.
> Where does EEGLAB convert the bdf data to uV.
> How is the conversion done?
>
> Sometimes in the eegplot() function under 'Value' i see values in the range
> of 9000-10000, (even if I use EEG.data matrix, the values are in this range)
> after filtering and resampling, i see different values in the range :
> 150-200. (I was looking at EOG channels recorded with BIOSEMI, sampled at
> 2048 Hz)
> Why does this happen?
> --
> Regards
> M Abigail
>
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