[Eeglablist] readbdf - big data set - convert to single?

[Alois Schloegl]

The biosig interface has multiple option to address this problem.
You can read only specified channels, and/or segments, and output the 
data as single type.


% select limited list of channels with CHANLIST,
% return data as single
HDR = sopen(filename,CHANLIST,'OUTPUT:SINGLE');

% read segment of length duration
duration = 1; 	% segment lenght
for k = 0:duration:NRrec*HDR.SPR/HDR.SampleRate,
	[dat, HDR] = sread(HDR, duration, start);
end;

% do not forget to close the file
HDR = sclose(HDR);



On 08/29/12 20:09, ANDREW HILL wrote:
> I would suggest downsampling first - 512 Hz (2 ms resolution in an ERP) should be fine, if that's sufficient for your needs.
>
> That'll speed things up remarkably :)  You can use "Decimator" from Biosemi to do this before you import, if you want.
>
> Also, I tend to use "Converter" to move BDF files into EDF+ format before importing into Matlab.  This essentially applies a 0.016 Hz highpass filter, discarding the DC offset and making much smaller files.
>
> Lastly, your CPU and operating system both need to be 64-bit versions (as does your Matlab) if you want to ever be able to use more than 2GB of RAM - I'm assuming you are running out of RAM even with a lot of it and 64-bit, but just in case that's another gotcha.
>
>
>
> Best,
>
> andrew
>
>
>
>
> On Today 12:49 AM, davidebaldo84 at gmail.com wrote:
>
> Dear all,
> Lately I have been working with an EEG dataset containing 64 channels (sampling rate: 2048Hz, Biosemi data).When importing the data into Matlab (via pop_readbdf function) I experience two problems:
> 1. It takes a lot of time to load and afterwards the pc became extremely slow (I assume that is because of the huge amount of  RAM needed)2. Sometimes the pc run out of memory
>
> Thus I have modified the readbdf function, converting the EEG data from double to single precision (each value occupies 4 bytes instead of 8 bytes):
>     ... (line 100)   catch,           warning backtrace off;           warning('Warning: file might be incomplete');           Records(nrec:end) = [];           DAT.Record(RecLen*length(Records)+1:end,:) = [];           S(nrec:end,:) = [];           break;       end;
>   (line 109)  end;
> %%%%%%% START DAVIDE MODIFICATION %%%%%%%%
>   >>>>>>>      DAT.Record = single(DAT.Record);<<<<<<<  CONVERTING THE EEG DATA FROM DOUBLE TO SINGLE
> %%%%%%% END DAVIDE  MODIFICATION  %%%%%%%%
>
> if rem(Mode,2)==0% AutocalibDAT.Record=[ones(RecLen*length(Records),1) DAT.Record]*EDF.Calib;end;
> DAT.Record=DAT.Record';
> ..
>
> This way the data importing is much faster. The question is: Do you think I can have any problem because of converting EEG data from double to single precision?
>
> Thanks a lot,
>
> Davide.
>
>
>
>
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