BDF to EDF Converter

schmid · Post by **schmid** » Tue Jun 16, 2009 8:42 am

Hello Mr COEN,

We are using strain gage sensors plugged on the ERGO1 channel of the AD-box. The range of these channels is 10 Volts, or 1 Volts.

While converting data from BDF to EDF with our BDF2EDF converter program, these channels are clipped (truncated ?) (of course, these channels are not clipped in the original EDF files). We can choose the resolution we want to use for the conversion, but the values are not enought high ...

Is it a way to convert our strenght data without having their highest values truncated ?
Have we to modify some acquisition parameters to avoid this convertion problem ?
Should we use an other convertion program ?

Thanks !

Post by **Coen** » Tue Jun 16, 2009 5:54 pm

For the force channels, the LSB value of the eventual EDF file should be a factor of 256 (2^(24-16) higher than the LSB value of the original BDF file.

LSB value on the EEG channels should be kept under approx. 1 uV to ensure sufficient dithering (without dithering, you won't be able to calculate ERPs anymore, see http://www.biosemi.com/faq/smallest_bitstep.htm)

Best regards, Coen (BioSemi)

schmid · Post by **schmid** » Tue Jun 23, 2009 3:28 pm

I understand that the force channels and EEG channels can't have the same LSB value (the first is in Volt, the other in µVolts)...

So we could convert these channels separtely to have a good resolution for each one, but ... the listbox of LSB value in the BDF2EDF converter is not enough high to convert the Force channels ...

How can we manage to convert Force channels in Volts from a BDF file to an EDF file ??

Post by **Coen** » Thu Jun 25, 2009 9:52 am

The EEG channels and the AIB channels both use uV as unit (see file header). The difference is that the EEG channels use a LSB = 31.25 nV, whereas the Ergo channels use LSB = 125 nV

I understand that you have written you own BDF --> EDF converter, or that you have modified my program from http://www.biosemi.com/download/Converter.zip. If should then be straight forward to process the Ergo channels with the proper parameters (no high pass, new LSB = 32 uV).

Best regards, Coen (BioSemi)

schmid · Post by **schmid** » Wed Jul 01, 2009 1:44 pm

Sorry, but we are using your bdf2edf converter (converter82.exe from 27/03/2007, which is the last version in your download section) and the available values for the LSB range from 31.25nV to 1 µV ... so how can I set the LSB of the ergo channels at 32 µV ?? and the highpass can't be removed, it only can be set à 0.01 Hz

Thanks

Post by **Coen** » Fri Jul 03, 2009 2:45 pm

The converter is a simple open-source program (in LabVIEW). You will have to make some changes to the code to process the Ergo channels differently form the EEG channels. Please contact me directly for detailed advise on the Lab VIEW changes.

Why is the conversion to EDF necessary ?

Best regards, Coen (BioSemi)

schmid · Post by **schmid** » Mon Jul 06, 2009 8:05 am

We have not labview

We need to convert to EDF because we are using BrainVision Software to analyse EEG's ...

Thanks

Post by **Coen** » Tue Jul 07, 2009 10:52 am

Please sent me an example file (few seconds is enough), and I will make a custom version of the converter for your special application.

Best regards, Coen (BioSemi)

schmid · Post by **schmid** » Tue Jul 07, 2009 3:16 pm

I send you a file at info@biosemi.com

Thanks again !