<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Dear Marco,<div><br></div><div>Your calculation is correct. EEGLAB uses the pwelch Matlab for computing power in STUDY (and for single datasets as well) by default. Power in pwelch is in dB/rad/sample so this might be at the source of the scaling problem you are encountering. You might want to look at the Matlab discussion lists on this subject.</div><div>Best regards,</div><div><br></div><div>Arno</div><div><br><div><div>On Jul 11, 2012, at 9:24 AM, Marco Montalto wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Any feedback re. problem below?<div><br></div><div>Thanks!</div><div><br></div><div>Marco<br><div><div>On 09 May 2012, at 20:27, Marco Montalto wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Dear Arnaud,<div><br></div><div>By any chance have you any feedback regarding the problem I reported in an earlier email (pasted below)? Thanks a lot for all the advise you may give me.</div><div><br></div><div>Regards,</div><div>Marco<br><div><br><div>Begin forwarded message:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px;"><span style="font-family:'Helvetica'; font-size:medium; color:rgba(0, 0, 0, 1.0);"><b>From: </b></span><span style="font-family:'Helvetica'; font-size:medium;">Marco Montalto <<a href="mailto:montaltomarco@onvol.net">montaltomarco@onvol.net</a>><br></span></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px;"><span style="font-family:'Helvetica'; font-size:medium; color:rgba(0, 0, 0, 1.0);"><b>Subject: </b></span><span style="font-family:'Helvetica'; font-size:medium;"><b>Fwd: Very large amplitude values - STUDY design</b><br></span></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px;"><span style="font-family:'Helvetica'; font-size:medium; color:rgba(0, 0, 0, 1.0);"><b>Date: </b></span><span style="font-family:'Helvetica'; font-size:medium;">18 March 2012 18:51:50 GMT+01:00<br></span></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px;"><span style="font-family:'Helvetica'; font-size:medium; color:rgba(0, 0, 0, 1.0);"><b>To: </b></span><span style="font-family:'Helvetica'; font-size:medium;">Arnaud Delorme <<a href="mailto:arno@ucsd.edu">arno@ucsd.edu</a>><br></span></div><br><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">In reference to my previous email, I am hereby adding an example from Channel Fp1, Subject 1, Condition 1, at 8 Hz:<div><br></div><div>Power value, log (dB) scaled:
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</tbody></table><div><br></div><div>Power value, now transformed to absolute power value (10^(Value/10):</div>
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</tbody></table><div><br></div><div>Square root of the above absolute power value in order to get amplitude:</div><div><br></div>
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<td height="15" align="right" width="65" style="height:15.0pt;width:65pt">517.1302798<br><br><br></td>
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</tbody></table><div>One question: should I be moving the decimal point by one maybe? Because then the amplitude values make sense.</div><div><br></div><div>Thanks very much and looking forward to your reply.</div><div><br></div><div>Regards,</div><div>Marco</div><div> <br><div>Begin forwarded message:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px;"><span style="font-family:'Helvetica'; font-size:medium; color:rgba(0, 0, 0, 1.0);"><b>From: </b></span><span style="font-family:'Helvetica'; font-size:medium;">Marco Montalto <<a href="mailto:montaltomarco@onvol.net">montaltomarco@onvol.net</a>><br></span></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px;"><span style="font-family:'Helvetica'; font-size:medium; color:rgba(0, 0, 0, 1.0);"><b>Subject: </b></span><span style="font-family:'Helvetica'; font-size:medium;"><b>Very large amplitude values - STUDY design</b><br></span></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px;"><span style="font-family:'Helvetica'; font-size:medium; color:rgba(0, 0, 0, 1.0);"><b>Date: </b></span><span style="font-family:'Helvetica'; font-size:medium;">17 March 2012 12:13:27 GMT+01:00<br></span></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px;"><span style="font-family:'Helvetica'; font-size:medium; color:rgba(0, 0, 0, 1.0);"><b>To: </b></span><span style="font-family:'Helvetica'; font-size:medium;">Arnaud Delorme <<a href="mailto:arno@ucsd.edu">arno@ucsd.edu</a>><br></span></div><br><div>Dear Arnaud,<br><br>I have just one more question: in STUDY design, after extracting the log(dB) scaled power values from 8-13 Hz (with a bin resolution of 0.5 Hz) and then transforming the values into absolute power values (10^(Power Value/10), if I then take the square root of the resulting values to check the amplitude, the values are very high, beyond 150 microvolts, even though I am 100% sure that none of the epochs exceed ±100 microvolts. Would you know why this is so? Am I missing out something?<br><br>Thanks once again for any information you may supply me with.<br><br>Regards,<br>Marco</div></blockquote></div><br></div></div></blockquote></div><br></div></div></blockquote></div><br></div></div></blockquote></div><br></div></body></html>