GDF files not obtaining Sample Rate?

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dsuares
Posts: 2
Joined: Thu Jun 22, 2017 8:20 pm

GDF files not obtaining Sample Rate?

Post by dsuares »

Hi all,

We've observed an issue importing GDF files converted from EEGLAB to Openvibe. This happens regardless of whether the source file is .EEG or .EDF. The 3d and 2d topographic map is generated correctly, but the Power spectrum display and time frequency map display are not showing, with no errors. We believe that this is because the GDF's sample rate isn't being read into OpenVibe correctly("sampling frequency was estimated from the chunk size to be 0... Forcing the rate to 1"), which is seen as a warning in the console picture. I've already tried the following fix, which hasn't resolved the issue (unless I did it wrong?):
“Openvibe apparently manages GDF files in version V1.25. If you export EEG data from EEGLAB in a GDF file, this will be created using the gdf 2.11 version, which is not readable by Openvibe (you get the warning message indicating the presence of channels with different sampling rates). As a simple workaround, just modify the script writeeeg.m of EEGLAB like following :

HDR.VERSION = 2.11; ==> HDR.VERSION = 1.25;"

Here is the writeeeg.m, the GDF File and the scenario:
scenario: https://drive.google.com/file/d/0B1xYXD ... sp=sharing
tester gdf: https://drive.google.com/file/d/0B1xYXD ... sp=sharing
writeeg: https://drive.google.com/file/d/0B1xYXD ... sp=sharing

Thank you all in advance for your help,
Dominic Suares

jtlindgren
Posts: 778
Joined: Tue Dec 04, 2012 3:53 pm
Location: INRIA Rennes, FRANCE

Re: GDF files not obtaining Sample Rate?

Post by jtlindgren »

Hi Dominic,

I looked briefly at your files - the gdf seems to be ok (for example looks fine in signal display; I specced chunk size of 50 in the GDF Reader). What you have is a problem of scenario design,

- The power spectrum display and time frequency map display would both like their input from the amplitude socket of the FFT box
- The reason the 2D and 3D boxes complain is the signal processing on the right hand side; these boxes apparently expect to get continuous, nonoverlapping data. What they do when the data overlaps would need to analyze the source code (unfortunately I dont have the time for that)


Cheers,
Jussi

dsuares
Posts: 2
Joined: Thu Jun 22, 2017 8:20 pm

Re: GDF files not obtaining Sample Rate?

Post by dsuares »

jtlindgren wrote:Hi Dominic,

I looked briefly at your files - the gdf seems to be ok (for example looks fine in signal display; I specced chunk size of 50 in the GDF Reader). What you have is a problem of scenario design,

- The power spectrum display and time frequency map display would both like their input from the amplitude socket of the FFT box
- The reason the 2D and 3D boxes complain is the signal processing on the right hand side; these boxes apparently expect to get continuous, nonoverlapping data. What they do when the data overlaps would need to analyze the source code (unfortunately I dont have the time for that)


Cheers,
Jussi
Hi Jussi,

Thank you for looking into it! What would be the correct way to organize the PSD and TF map display boxes so that they display correct? Can the FFT box not provide amplitude to two different displays?

jtlindgren
Posts: 778
Joined: Tue Dec 04, 2012 3:53 pm
Location: INRIA Rennes, FRANCE

Re: GDF files not obtaining Sample Rate?

Post by jtlindgren »

Hello,

you can definitely connect one output to several inputs in openvibe to route the same data to different displays.
I recommend taking a look at the scenarios in box-tutorials/ folder and mimic from there; look for files
with fft, map or power spectrum as parts of the filenames.



Happy hacking,
Jussi

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