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<div class="moz-cite-prefix">Hi Yun,<br>
<br>
Detrending a data set only removes the regression line. It does
not ensure that the process has zero mean, which translates to a
zero DC component in frequency space. The most direct way to
ensure zero DC is simply to remove the trial mean from each
epoch. <br>
<br>
Best,<br>
<br>
Alexander<br>
<pre class="moz-signature" cols="72">Alexander Nakhnikian, Ph.D.
Post Doctoral Fellow, Clinical Research Training Program
Harvard Medical School
Boston VA Healthcare System, Brockton MA</pre>
On 12/5/14, 4:20 PM, Yun Wen wrote:<br>
</div>
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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>
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</pre>
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