Thanks a lot for your answers!<div><br></div><div>@Chris: When I convert, the EEG data (DAT.Record) are still double and the following command takes a lot of time and RAM to run. But with the conversion to single precision it become much faster:</div>
<div><br></div><div><div>if rem(Mode,2)==0<span class="Apple-tab-span" style="white-space:pre"> </span>% Autocalib</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>DAT.Record=[ones(RecLen*length(Records),1) DAT.Record]*EDF.Calib;</div>
<div>end; </div><div><br></div><div>I need to load the entire set of data (to run ICA for example). I have no problem loading with the conversion to single precision, but I would like to know if anyone think that the EEG data should not be converted from double to single precision ( I had no problem so far)</div>
<div><br></div><div><br></div><div>@Andrew: I agree with you, 512Hz would be enough. But I prefer to record at 2048Hz and resampling the data via software after importing them into Matlab. (that is why I need to load them first).</div>
<div>The converted option sounds interesting, but could you please explain why files became smaller after removing the DC offset? I believe that even without offset the data would be represented in double precision, thus each sample still need 8 bytes.</div>
<div>(yes, I am using a quadcore 64-bit laptop with 4GB of RAM, even though I have the impression that is hard to take advantage of having 4 processors, unless you use parallel processing).</div><div><br></div><div><br></div>
<div>Thanks again!</div><div><br></div><div>Davide.</div><div><br></div><div><br></div><br><div class="gmail_quote">On Wed, Aug 29, 2012 at 8:09 PM, ANDREW HILL <span dir="ltr"><<a href="mailto:andrewhill@ucla.edu" target="_blank">andrewhill@ucla.edu</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><p>I would suggest downsampling first - 512 Hz (2 ms resolution in an ERP) should be fine, if that's sufficient for your needs.</p>
<p>That'll speed things up remarkably :) You can use "Decimator" from Biosemi to do this before you import, if you want.</p><p>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.</p>
<p>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.</p>
<p> </p><p>Best,</p><p>andrew</p><div class="HOEnZb"><div class="h5"><p> </p><p><br>On Today 12:49 AM, <a href="mailto:davidebaldo84@gmail.com" target="_blank">davidebaldo84@gmail.com</a> wrote: <br><br>Dear all,</p><div>
<br></div><div>Lately I have been working with an EEG dataset containing 64 channels (sampling rate: 2048Hz, Biosemi data).</div><div>When importing the data into Matlab (via pop_readbdf function) I experience two problems:</div>
<div><br></div><div>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)</div><div>2. Sometimes the pc run out of memory</div><div><br>
</div><div><br></div><div>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):</div><div><br></div><div> ...</div><div><div>
(line 100) catch,</div><div> warning backtrace off;</div><div> warning('Warning: file might be incomplete');</div><div> Records(nrec:end) = [];</div><div> DAT.Record(RecLen*length(Records)+1:end,:) = [];</div>
<div> S(nrec:end,:) = [];</div><div> break;</div><div> end;</div><div><br></div><div> (line 109) end;</div><div><br></div><div>%%%%%%% START DAVIDE MODIFICATION %%%%%%%%</div><div><br></div><div>
>>>>>>> DAT.Record = single(DAT.Record); <<<<<<< CONVERTING THE EEG DATA FROM DOUBLE TO SINGLE</div><div><br></div><div>%%%%%%% END DAVIDE MODIFICATION %%%%%%%% </div><div>
<br></div><div><br></div><div>if rem(Mode,2)==0<span style="white-space:pre-wrap"> </span>% Autocalib</div><div><span style="white-space:pre-wrap"> </span>DAT.Record=[ones(RecLen*length(Records),1) DAT.Record]*EDF.Calib;</div>
<div>end; </div><div><br></div><div>DAT.Record=DAT.Record';</div></div><div><br></div><div>...</div><div><br></div><div><br></div><div>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?</div>
<div><br></div><div><br></div><div>Thanks a lot,</div><div><br></div><div><br></div><div>Davide.</div>
</div></div></blockquote></div><br></div>