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Hi to all who’s reading along,
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<div class="">Perhaps the two cases will become more similar once the ‘timwin’ is increased in length for the mtmconvol case….</div>
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<div class="">Best wishes,</div>
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<div class="">JM</div>
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<div class="">On 20 Sep 2017, at 16:26, Robert Oostenveld <<a href="mailto:r.oostenveld@donders.ru.nl" class="">r.oostenveld@donders.ru.nl</a>> wrote:</div>
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Hi Vladimir,
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<div class="">I suggest that you first start with a simpler case, like this</div>
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<div class=""><font face="Courier" class="">fsample = 1000;</font></div>
<div class=""><font face="Courier" class="">time = (1:1000)/fsample;</font></div>
<div class=""><font face="Courier" class="">dat = randn(size(time));</font></div>
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</font></div>
<div class=""><font face="Courier" class="">[spectrum1,ntaper1,freqoi1] = ft_specest_mtmfft(dat, time, 'taper', 'hanning');</font></div>
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</font></div>
<div class=""><font face="Courier" class="">power1 = abs(spectrum1).^2;</font></div>
<div class=""><font face="Courier" class="">power1 = squeeze(power1);</font></div>
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</font></div>
<div class=""><font face="Courier" class="">[spectrum2,ntaper2,freqoi2,timeoi2] = ft_specest_mtmconvol(dat, time, 'taper', 'hanning', 'timeoi', mean(time), 'timwin', 0.5);</font></div>
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<div class=""><font face="Courier" class="">power2 = abs(spectrum2).^2;</font></div>
<div class=""><font face="Courier" class="">power2 = squeeze(power2);</font></div>
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</font></div>
<div class=""><font face="Courier" class="">figure</font></div>
<div class=""><font face="Courier" class="">plot(freqoi1, power1);</font></div>
<div class=""><font face="Courier" class="">hold on</font></div>
<div class=""><font face="Courier" class="">plot(freqoi2, power2, 'r');</font></div>
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<div class="">Note that these are not the same (albeit similar), which I had expected…</div>
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<div class="">best</div>
<div class="">Robert</div>
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<div class="">On 20 Sep 2017, at 12:56, Vladimir Litvak <<a href="mailto:litvak.vladimir@gmail.com" class="">litvak.vladimir@gmail.com</a>> wrote:</div>
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<div dir="ltr" class="">Dear Fieldtrippers,
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<div class="">I'm looking into an issue of one of SPM users who gets different results when doing TF decomposition compared to computing a spectrum for the same time window. I'm not sure I got to the bottom of it yet but one thing I found is that ft_specest_mtmfft
and ft_specest_mtmconvol are affected differently by increasing padding. For short padding the results are similar but with increasing padding there are differences both in offset of the spectrum and its overall shape. See attached images where the top one
shows original spectra and the bottom one aligns the lowermost bin to zero. </div>
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<div class="">Is this a bug or a feature?</div>
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<div class="">Below is the script that produces these plots. I could provide the data as well but this could probably be reproduced with any data.</div>
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<div class="">Thanks,</div>
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<div class="">Vladimir</div>
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<div class="">pad = 0.5;%1%10</div>
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<div class="">freqoi = 5:45;</div>
<div class="">timwin = 0.4+0*freqoi;</div>
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<div class="">[spectrum,ntaper,freqoi,timeoi] = ft_specest_mtmconvol(data, time, 'taper', 'hanning', 'timeoi', 1.2, 'freqoi', freqoi,...</div>
<div class=""> 'timwin', timwin, 'tapsmofrq', 1, 'verbose', 0, 'pad', pad);</div>
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<div class="">s1 = squeeze(mean(mean(abs(spectrum), 4), 2));</div>
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<div class="">figure;</div>
<div class="">subplot(2,1,1)</div>
<div class="">plot(freqoi, s1);</div>
<div class="">subplot(2,1,2);</div>
<div class="">plot(freqoi, s1-s1(1));</div>
<div class="">%%</div>
<div class="">[spectrum,ntaper,freqoi] = ft_specest_mtmfft(data, time, 'taper', 'hanning', 'freqoi', freqoi,...</div>
<div class=""> 'tapsmofrq', 1, 'verbose', 0, 'pad', pad);</div>
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<div class="">s2 = squeeze(mean(mean(abs(spectrum), 2), 1));</div>
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<div class="">subplot(2,1,1)</div>
<div class="">hold on</div>
<div class="">plot(freqoi, s2, 'r');</div>
<div class="">subplot(2,1,2)</div>
<div class="">hold on</div>
<div class="">plot(freqoi, s2-s2(1), 'r');</div>
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<span id="cid:644C10BA-EE23-4C79-817F-AED817ACCF00@ki.se" class=""><pad0_5.png></span><span id="cid:0A594045-C414-4F44-90FF-32D0857460C8@ki.se" class=""><pad1.png></span><span id="cid:6709F946-F5E8-4614-AA94-A53AEFA36EFA@ki.se" class=""><pad10.png></span>_______________________________________________<br class="">
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