<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Hi folks,<div><br></div><div>I'm trying to filter some MEG data sampled at 200Hz using ft_preproc_highpassfilter. It seems to be behaving slightly strangely. I'm calling it with</div><div>Fs = 200;</div><div>Fhp = 5;</div><div>N = 6;</div><div><br></div><div>and a stretch of single-channel data with ~50000 samples. However, the returned data doesn't seem to be filtered at 5Hz. </div><div><br></div><div>When I go into the code and use fvtool to look at the frequency response of the filter, it doesn't have the shape I was expecting:</div><div><br></div><div style="font-size: 13px; "><img height="107" width="320" apple-width="yes" apple-height="yes" id="48a7d8a1-41b6-4f48-b4a6-f8fb926d1900" src="cid:141BD0AF-F7D1-41A4-A45E-E0F5ED790175@fmrib.ox.ac.uk"></div><div><br></div><div>I wondered whether this was because of the GNU public license version of butter that was being called by fieldtrip (in preproc/private), so I took this out of my matlab path and let it find the Mathworks' butter.m, from the signal processing toolbox. This seemed to give a more sensible looking filter design in fvtool:</div><div><br></div><div><img height="107" width="320" apple-width="yes" apple-height="yes" id="6a83c29e-06a4-4aaf-bf1d-e3d203c96549" src="cid:B789F424-54C8-48AE-9D89-39D4EC7679EF@fmrib.ox.ac.uk"></div><div><br></div><div>The Mathworks' butter.m also seemed to filter the data a bit more like I was expecting. Is this a problem with the GPL version, or am I calling the function wrong?</div><div><br></div><div>Cheers,</div><div>Laurence</div><div><br></div><div><br><div>
<span class="Apple-style-span" style="font-size: 12px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div class="AppleMailSignature" id="17D31EC3-297A-4FA6-B7EE-EE06DE0A8243"><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">===========================================</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Laurence Hunt, DPhil Student</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "> Centre for Functional MRI of the Brain (FMRIB), </div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">University of Oxford</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><a href="mailto:lhunt@fmrib.ox.ac.uk">lhunt@fmrib.ox.ac.uk</a></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Phone: (+44)1865-(2)22738</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">===========================================</div></div></div></div></div></span></div></span></div></span>
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