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Hi Adam,
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<div class="">What’s your question? I have some difficulty distilling it from your e-mail. </div>
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<div class="">I assume that you have visited the discussion list’s archive, where you will have noticed that questions regarding the units of the output of ft_freqanalysis pop up now and then. </div>
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<div class="">Nobody seems to have made an effort so far, to sort it out once and for all, by making a FAQ out of this. I think it would be great if you could start this piece of documentation by describing the normalisation that FT uses in ft_freqanalysis
(and the underlying ft_specest_<> functions), and how this relates to plain matlab, or any other software package. </div>
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<div class="">Perhaps you could start by studying the difference between the power spectrum, and power spectral density. The fact that you use the term PSD in your e-mail, whereas - as far as I know - fieldtrip does not use this terminology, nor claims that
it computes the PSD. </div>
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<div class="">Good luck,</div>
<div class="">Jan-Mathijs</div>
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<div class="">On 11 Apr 2023, at 09:09, Adam Grinberg via fieldtrip <<a href="mailto:fieldtrip@science.ru.nl" class="">fieldtrip@science.ru.nl</a>> wrote:</div>
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<span lang="EN-GB" class="">Hello,<span class="Apple-converted-space"> </span><o:p class=""></o:p></span></div>
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<span lang="EN-GB" class="">My question concerns the Fieldtrip PSD function. I am running the code on some EEG data and comparing it with the MATLAB periodogram function. While the FFT produces similar graphical shape of the spectrogram, the units are different.<span class="Apple-converted-space"> </span><o:p class=""></o:p></span></div>
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<span lang="EN-GB" class="">The periodogram function’s units are µV^2/Hz, which is the common output for power (before converting to Db). However, the values that I get with the Fieldtrip freqanalysis function seem to be ~120 times lower. I cannot understand
what they are. I looked at the code and still do not get it. I suppose that this is due to some normalization method done but I am not certain as to the rationale for the particular one used.<o:p class=""></o:p></span></div>
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<span lang="EN-GB" class=""><o:p class=""> </o:p></span></div>
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<span lang="EN-GB" class="">Tanks.<o:p class=""></o:p></span></div>
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<span lang="EN-GB" class=""><o:p class=""> </o:p></span></div>
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<span lang="EN-GB" class=""><o:p class=""> </o:p></span></div>
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<span lang="EN-GB" style="font-size: 16pt; font-family: Mistral;" class="">/Adam</span><span lang="EN-GB" class=""><o:p class=""></o:p></span></div>
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<span lang="EN-GB" style="font-family: "Arial Nova", sans-serif; color: rgb(127, 127, 127);" class="">______________________________________________________________________________________</span><span lang="EN-GB" class=""><o:p class=""></o:p></span></div>
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<span lang="EN-GB" style="font-family: "Arial Nova", sans-serif; color: rgb(127, 127, 127);" class="">Adam Grinberg, PT, PhD</span><span lang="EN-GB" class=""><o:p class=""></o:p></span></div>
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<span lang="EN-GB" style="font-family: "Arial Nova", sans-serif; color: rgb(127, 127, 127);" class="">Department of Community Medicine and Rehabilitation, Physiotherapy</span><span lang="EN-GB" class=""><o:p class=""></o:p></span></div>
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<span style="font-family: "Arial Nova", sans-serif; color: rgb(127, 127, 127);" class="">Umeå University<o:p class=""></o:p></span></div>
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<span style="font-family: "Arial Nova", sans-serif; color: rgb(127, 127, 127);" class="">Umeå, Sweden<o:p class=""></o:p></span></div>
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<span style="font-family: "Arial Nova", sans-serif; color: rgb(127, 127, 127);" class="">Tel: +46 (0) 90 786 96 30<o:p class=""></o:p></span></div>
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<o:p class=""> </o:p></div>
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<span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">_______________________________________________</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class="">
<span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">fieldtrip
mailing list</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class="">
<a href="https://mailman.science.ru.nl/mailman/listinfo/fieldtrip" style="font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" class="">https://mailman.science.ru.nl/mailman/listinfo/fieldtrip</a><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class="">
<a href="https://urldefense.com/v3/__https://doi.org/10.1371/journal.pcbi.1002202__;!!HJOPV4FYYWzcc1jazlU!5RV3s_lQGO_tsuGgo7zcEBucW8cr1i6mPkGsevulfd0lqL2ZKYY1PEjFVCEckP4wN0npvpixDOgKahPY-LyhBMYq7EeOEcRI1EwbUA$" style="font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" class="">https://urldefense.com/v3/__https://doi.org/10.1371/journal.pcbi.1002202__;!!HJOPV4FYYWzcc1jazlU!5RV3s_lQGO_tsuGgo7zcEBucW8cr1i6mPkGsevulfd0lqL2ZKYY1PEjFVCEckP4wN0npvpixDOgKahPY-LyhBMYq7EeOEcRI1EwbUA$</a><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class=""></span></div>
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