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<div class="moz-cite-prefix">It looks as though the take home
message is that in theory high pass filters remove DC but you
can't be sure how they will interact with empirical data since
there is no perfect filter in the real world. If other people
report substantial artifacts after filtering data without removing
the DC component I suggest getting rid of it. To answer your
original question, assuming you're detrending each epoch
individually it should remove the DC component or at least reduce
it substantially. <br>
<br>
I hope that helps.<br>
<br>
<br>
<br>
On 12/5/14, 6:20 PM, Yun Wen wrote:<br>
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<p class="MsoNormal"><span style="color:#1F497D">Hi, Alexander
& Rodrigo. Thank you very much for your help. I
collected my data with DC recordings (BioSemi system). I
have seen some discussion on the DC offset:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><a class="moz-txt-link-freetext" href="http://sccn.ucsd.edu/pipermail/eeglablist/2014/008068.html">http://sccn.ucsd.edu/pipermail/eeglablist/2014/008068.html</a><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><a class="moz-txt-link-freetext" href="http://sccn.ucsd.edu/pipermail/eeglablist/2008/002229.html">http://sccn.ucsd.edu/pipermail/eeglablist/2008/002229.html</a><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><a class="moz-txt-link-freetext" href="http://sccn.ucsd.edu/pipermail/eeglablist/2010/003315.html">http://sccn.ucsd.edu/pipermail/eeglablist/2010/003315.html</a><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><a class="moz-txt-link-freetext" href="http://erpinfo.org/erplab/erplab-documentation/manual/Filtering.html">http://erpinfo.org/erplab/erplab-documentation/manual/Filtering.html</a><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">It seems to me
that I’d better remove DC offset of continuous data before
high-pass filter. Am I right?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Best,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Yun<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
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<div style="border:none;border-top:solid #E1E1E1
1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal"><b><span style="color:windowtext">From:</span></b><span
style="color:windowtext">
<a class="moz-txt-link-abbreviated" href="mailto:fieldtrip-bounces@science.ru.nl">fieldtrip-bounces@science.ru.nl</a>
[<a class="moz-txt-link-freetext" href="mailto:fieldtrip-bounces@science.ru.nl">mailto:fieldtrip-bounces@science.ru.nl</a>] <b>On Behalf
Of </b>Alexander Nakhnikian<br>
<b>Sent:</b> Friday, December 05, 2014 10:19 PM<br>
<b>To:</b> FieldTrip discussion list<br>
<b>Subject:</b> Re: [FieldTrip] about detrend<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<div>
<p class="MsoNormal">Hello Again,<br>
<br>
I think there's an error in my response. I think removing
the linear trend should also set the mean to zero already
since the best fit line incorporates vertical offset. Sorry
about that. <br>
<br>
A<br>
<br>
<span style="font-size:12.0pt"><o:p></o:p></span></p>
<pre><o:p> </o:p></pre>
<p class="MsoNormal">On 12/5/14, 4:20 PM, Yun Wen wrote:<o:p></o:p></p>
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<p class="MsoNormal">Hi all, I want to remove DC offset before
applying the high-pass filter. I was wondering if I can
achieve that by putting cfg.detrend = 'yes' before
cfg.hpfilter = 'yes', something like:<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">cfg = []; <o:p></o:p></p>
<p class="MsoNormal">cfg.dataset = filename_raweeg;<o:p></o:p></p>
<p class="MsoNormal">cfg.detrend = 'yes'; <o:p></o:p></p>
<p class="MsoNormal">cfg.hpfilter = 'yes';<o:p></o:p></p>
<p class="MsoNormal">cfg.hpfiltord = 2; % Order of the filter
= 2.<o:p></o:p></p>
<p class="MsoNormal">cfg.hpfreq = 0.1; % High-pass cutoff at
0.1 Hz;<o:p></o:p></p>
<p class="MsoNormal">[data] = ft_preprocessing (cfg);<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">Thank you in advance.<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">Best,<o:p></o:p></p>
<p class="MsoNormal">Yun<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<pre><o:p> </o:p></pre>
<pre><o:p> </o:p></pre>
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