<div dir="ltr"><div><div><div><div><div><div><div><div>Unfortunatelly, that's the basic <span class="">time/frequency trade-off - if you want to <br>resolve frequencies that are closer than your frequency resolution<br>
</span></div><span class="">you need a longer singnal sample (longer analysis window).<br></span></div><span class="">At least this is the case for standard methods like FFT.<br></span></div><span class=""><br>There are also so-called 'parametric' methods that are said to overcome<br>
</span></div><span class="">some of the limitations of the classical methods (see for example MUSIC<br></span></div><span class="">algorithm), but are less general (require some prior knowledge about the<br></span></div><span class="">signal). I have never used any of these methods however, so I cannot<br>
tell you more than that they exist :)<br><br></span></div><span class="">And then - it depends on what you are trying to examine in the signal.<br></span></div><span class="">Maybe extending analysis window and/or using padding will be satisfactory.<br>
<br></span><div><div><span class=""><br></span><div><div><div><div><div><div><span class=""><br></span></div></div></div></div></div></div></div></div></div><div class="gmail_extra"><br clear="all"><div>Pozdrawiam,<br>Mikołaj Magnuski</div>
<br><br><div class="gmail_quote">2013/9/13 Steven Pillen <span dir="ltr"><<a href="mailto:stevendpillen@gmail.com" target="_blank">stevendpillen@gmail.com</a>></span><br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">That is, without interpolation (which probably isn't ideal for the kind of things I'm trying to see)?<div><div class="h5"><div class="gmail_extra"><br><br><div class="gmail_quote">On Fri, Sep 13, 2013 at 11:02 AM, Steven Pillen <span dir="ltr"><<a href="mailto:stevendpillen@gmail.com" target="_blank">stevendpillen@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">So there's no way to get smaller frequency windows with an epoch size that small?<div><div>
<div class="gmail_extra"><br><br><div class="gmail_quote">On Wed, Sep 11, 2013 at 5:56 PM, Mikołaj Magnuski <span dir="ltr"><<a href="mailto:imponderabilion@gmail.com" target="_blank">imponderabilion@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><p dir="ltr"><br>
Hi Steven,</p>
<p dir="ltr">Frequency resolution depends on window size, so what you're seeing is normal.<br>
However, for visualisation purposes you can interpolate the spectrum (which is implemented by zero-padding your data to some desired length) - EEGlab functions allow to specify the degree of this smoothing. <br>
For example you can control the zero-padding in spectopo function with 'nfft' (specific length to zero-pad the data to). <br>
By specifying 'nfft' to be two times the number of samples in your analysis window you increase the frequency resolution twofold (although you have to remember that this is not a genuine increase in frequence resolution but an interpolation).</p>
<p dir="ltr">Also, see the help messages to pop_spectopo and spectopo functions.</p>
<p dir="ltr">For time-frequency you can use the 'nfreqs' key in newtimef.m to control the frequency resolution<br>
</p>
<div class="gmail_quote">12 wrz 2013 01:27, "Steven Pillen" <<a href="mailto:stevendpillen@gmail.com" target="_blank">stevendpillen@gmail.com</a>> napisał(a):<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div><div>
<div dir="ltr">Hello, EEGLABlist.<div><br></div><div>When we ran power spectrum measures through the study functions on files whose epochs were about 0.2 seconds long, it looked like the power spectra chart generated had very few points of reference. Looking at the .datspec files using the function </div>
<div><i><br></i></div><div><i>m = importdata('design1_2003_regular.datspec')</i></div><div><i><br></i></div><div>in m.freqs, it looked like there was one bin for every 5 hz, which matched what the charts looked like. </div>
<div><br></div><div>We ran the same data again, this time cut into 1 second epochs, and the power spectra looked like they had many more reference points. Likewise, there appeared to be a bin in m.freqs for every 1 hz. as opposed to the previous 5.</div>
<div><br></div><div>Is there any way to increase the number of bins with a smaller sized epoch so that the power spectra is more robust? </div></div>
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