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tutorial:natmeg:timefrequency [2018/10/21 15:10]
42.49.180.224 [Background]
tutorial:natmeg:timefrequency [2017/08/17 12:33] (current)
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 Calculating time-frequency representations of power is done using a sliding time window. This can be done according to two principles: either the time window has a fixed length independent of frequency, or the time window decreases in length with increased frequency. For each time window the power is calculated. Prior to calculating the power one or more tapers are multiplied with the data. The aim of the tapers is to reduce spectral leakage and control the frequency smoothing. ​ Calculating time-frequency representations of power is done using a sliding time window. This can be done according to two principles: either the time window has a fixed length independent of frequency, or the time window decreases in length with increased frequency. For each time window the power is calculated. Prior to calculating the power one or more tapers are multiplied with the data. The aim of the tapers is to reduce spectral leakage and control the frequency smoothing. ​
  
-{{tutorial:​timefrequencyanalysis:​tfrtiles.png?​600|"Figure 1; Time and frequency smoothing. (a) For a fixed length time window the time and frequency smoothing remains fixed. (b) For time windows that decrease with frequency, the temporal smoothing decreases and the frequency smoothing increases."}}+{{tutorial:​timefrequencyanalysis:​tfrtiles.png?​600|"Figure 1; Time and frequency smoothing. (a) For a fixed length time window the time and frequency smoothing remains fixed. (b) For time windows that decrease with frequency, the temporal smoothing decreases and the frequency smoothing increases."}}
  
 //Figure 1; Time and frequency smoothing. (a) For a fixed length time window the time and frequency smoothing remains fixed. (b) For time windows that decrease with frequency, the temporal smoothing decreases and the frequency smoothing increases.//​ //Figure 1; Time and frequency smoothing. (a) For a fixed length time window the time and frequency smoothing remains fixed. (b) For time windows that decrease with frequency, the temporal smoothing decreases and the frequency smoothing increases.//​
  
 If you want to know more about tapers/​window functions you can have a look at this  If you want to know more about tapers/​window functions you can have a look at this 
-[[http://​en.wikipedia.org/​wiki/​Window_function|wikipedia site]]. Note that Hann window is another name for Hanning window used in this tutorial. There is also a wikipedia site about multitapers,​ to take a look at it click [[http://​en.wikipedia.org/​wiki/​Multitaper|here]]. In this tutorial we will only look at Hanning tapers, and spend our time more in noticing the similarities and differences between MEG and EEG.+[[http://​en.wikipedia.org/​wiki/​Window_function|wikipedia site]]. Note that Hann window is another name for Hanning window used in this tutorial. There is also a wikipedia site about multitapers,​ to take a look at it click [[http://​en.wikipedia.org/​wiki/​Multitaper|here]]. In this tutorial we will only look at Hanning tapers, and spend our time more in noticing the similarities and differences between MEG and EEG.  
 ===== Procedure ===== ===== Procedure =====
  
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-This tutorial was last tested by Stephen with version 20140925 of FieldTrip using Matlab 2013b on a 64-bit CentOS platform.+This tutorial was last tested by Stephen with version 20140925 of FieldTrip using Matlab 2013b on a 64-bit CentOS platform. ​