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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Mori,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">This stems from the old days of clinical EEG amplifiers and analog filters. Historically, early EEGers used the concept of a time-constant, which basically
corresponded to the decay time (to half amplitude or 3 dB or the like) of an impulse applied to a simple resistor-capacitor (RC) filter. Typical time-constants were 1.0 or 0.1 seconds that were easy numbers for people to deal with. When the RC filter is considered
in more modern terms as a low-cut or high-pass filter, we shift to using Hz. Because of the math of sines and cosines, a factor of 2-pi gets applied, which leads to these funny numbers you mention.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">The above is all from memory, look it up on Google to get the particulars, and the exact conversion. Clinical EEG machines still give the user the option of
using time-constant or Hz for the lo-cut/hi-pass filter settings, even though no one uses simple RC filters anymore.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">-Jeff<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> eeglablist-bounces@sccn.ucsd.edu [mailto:eeglablist-bounces@sccn.ucsd.edu]
<b>On Behalf Of </b>mori larin<br>
<b>Sent:</b> Friday, February 20, 2015 5:22 AM<br>
<b>To:</b> eeglablist<br>
<b>Subject:</b> [Eeglablist] EEG filtering<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Dear all, <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I have a question about the low cut off frequency for EEG filtering.<o:p></o:p></p>
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<p class="MsoNormal">My question is why people select exactly 0.016 Hz and/or 0.16 Hz low cut off frequency?<o:p></o:p></p>
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<p class="MsoNormal">What do these value refer to and why exactly these values?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Many thanks,<o:p></o:p></p>
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<p class="MsoNormal">Mori <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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