[Eeglablist] .bdf data converted to microvolts

[Abigail Mani]

Dear Arno,

I tried what you suggested, but I see the same kind of high values.
But I think that it is not exactly a problem when we look at Bradley
Voytek's  reply:

*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*

Thanks
Abigail

2008/10/18 arno delorme <arno at ucsd.edu>

> Dear Abigail,
>
> are you using a custom program to record BDF files. We are using Alois
> Schlogl function in the BIOSIG toolbox
>
> http://biosig.sourceforge.net/
>
> to import data so I would first download the latest version of his toolbox
> to see if you still experience the problem when importing the data from the
> command line (sopen and sread functions) and then get back to him if you
> still experience problems.
>
> Best regards,
>
> Arno
>
>
> On 11 sept. 08, at 19:28, Abigail Mani 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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>


-- 
Regards
M Abigail
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