[Mne_analysis] combining/splitting fif files

Lauri Parkkonen lauri at neuro.hut.fi
Sun Feb 15 16:48:38 EST 2009
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Hi Eliezer,

The MEG system is deliberately splitting the files into 2-GB chunks as 
some systems and storage media have trouble handling files larger than 2 
GB. In addition, the current version of the fif format limits the file 
size to 2 GBs.

The 32-bit data format does mean somewhat more accurate recordings 
although in most measurements the benefit is marginal. However, the 
wider dynamic range is important when tackling with some unavoidable and 
strong interference signals, e.g., from patients with magnetic implants.

As Daniel wrote, just average the two files separately and then average 
the "subaverages", with appropriate weighting according to the number of 
trials you have in those subaverages. This latter averaging is easy to 
do in the Neuromag software (or in MNE).

Best regards,
Lauri

Eliezer Kanal wrote:
> Hello folks -
>
> I have an experimental paradigm which lasts approximately 40 minutes. 
> I usually just let the MEG run straight, end up with a single fif 
> file, and then do all my analysis on this. We recently switched from 
> 16 bit to a 32 bit architecture (side point: does this mean more 
> accurate recordings? what DOES that mean for the end user?), and I 
> learned something new: the machine will only save files less than 2 GB 
> in size. As such, I now have two files, myFile.fif (2 GB) and 
> myFile_1.fif (~1.6 GB). I have no idea where it split it, 
> behavioral-wise.
>
> What's the best way to proceed from here? I can't analyze them as they 
> sit, since I can't specify multiple files in mne_process_raw if the 
> files contain different numbers of trials. Is there a program that can 
> concatenate them? Should I just try to use mne_read_raw in matlab and 
> hope matlab doesn't choke on almost 4 GB of data? Any ideas? Thanks -
>
> Sincerely,
> Eliezer Kanal
> Graduate Student, Bioengineering
> Laboratory for Computational Neuroscience
> University of Pittsburgh
> 3520 Forbes Avenue, 2nd floor, R218
> Pittsburgh, PA 15213
> 412-802-6482
> Fax: 412-802-6785
>
>
>
>
>
>
>
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