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<body lang="EN-US" link="blue" vlink="purple">
<div class="WordSection1">
<p class="MsoNormal">Hi.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Is there someone out there with more details/understanding about<o:p></o:p></p>
<p class="MsoNormal">the filter design done by the ffilt command?<o:p></o:p></p>
<p class="MsoNormal">Specifically, for example, if one does <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoListParagraph">x=ffilt(“lp”,5,0.1)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l1 level1 lfo4"><![if !supportLists]><span style="font-family:Wingdings"><span style="mso-list:Ignore">n<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>the five coefficients are obviously not for a simple “boxcar” filter.<o:p></o:p></p>
<p class="MsoListParagraph">Is this a butterworth design? Is there a reference for what this<o:p></o:p></p>
<p class="MsoListParagraph">command is actually implementing?<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l2 level1 lfo1"><![if !supportLists]><span style="font-family:Wingdings"><span style="mso-list:Ignore">n<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>What is the definition of the cutoff frequency for ffilt?<o:p></o:p></p>
<p class="MsoListParagraph">If you take the above example and <o:p></o:p></p>
<p class="MsoListParagraph">[a,b] = frmag(x,500);<o:p></o:p></p>
<p class="MsoListParagraph">plot (a)<o:p></o:p></p>
<p class="MsoListParagraph">the first zero of amplitude is around 222 Hz, but the
<o:p></o:p></p>
<p class="MsoListParagraph" style="margin-left:.75in;text-indent:-.25in;mso-list:l0 level2 lfo2">
<![if !supportLists]><span style="mso-list:Ignore">0.1<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]>cutoff frequency would be at 100 Hz for 1000Hz sampling.<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in">Is the cutoff frequency defined as ln(2) of the DC response?<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l2 level1 lfo1"><![if !supportLists]><span style="font-family:Wingdings"><span style="mso-list:Ignore">n<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Why are the coefficients not normalized to give<o:p></o:p></p>
<p class="MsoListParagraph">a DC response amplitude of 1? Isn’t that the standard<o:p></o:p></p>
<p class="MsoListParagraph">approach for filter design?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks in advance.<o:p></o:p></p>
<p class="MsoNormal">G<o:p></o:p></p>
<p class="MsoListParagraph"><o:p> </o:p></p>
<p class="MsoListParagraph"><o:p> </o:p></p>
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