[Eeglablist] problems with bdf files

[Matt Craddock]

Hi Francesca,

The first problem is likely just because of the dynamic range of the 
BioSemi signals - the channels have very different DC offsets, so some 
are out of display range. For display purposes, when you're using the 
Channel Data Scroll, then selecting the Remove DC Offset option should 
make all the data re-appear. More generally this problem will disappear 
if you use a high-pass filter, or if you epoch the data and baseline 
correct it.

Second problem - best guess is you might have recorded from 263 channels 
even though you only had 32. It's perfectly possible to record empty 
channels if the recording software is set up incorrectly. In the 
pop_biosig interface it'll give you the option to choose which channels 
to load, so just do that - by default it will load all channels present 
in the recording. Check how your recording software is set up. Not sure 
what Cartool does on import or for display so, it's quite possible it's 
removing flatline channels, high-passing the data etc...

Cheers,
Matt

On 23/06/2017 10:11, Panin, Francesca wrote:
> Hi
> 
> I have problems opening some BDF files
> 
> I keep using the commands illustrated in the guidelines and each time I 
> obtain something different!
> 
> The problem is not in the file as I could open the data without problems 
> using another software called Cartool
> 
> I used the command Import data>From Biosemi BDF file and then I leave 
> the default options in the two subsequent dialogue boxes and I just click ok
> 
> What I obtain is either:
> 
> - I can see only one wave in the middle of the plot (but there are 32 
> channels)
> or
> - I obtain 263 channels (and, again, I should only have 32)
> 
> does anybody know how to help?
> 
> Thanks very much
> 
> Francesca
> 
> 
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