title: how to set the length of hanning window
body: <p>I have a time series of data in 6-hour interval.  I want to low-pass filter the data using hanning window with a cutoff period of 36h.</p>
  
  <p>The corresponding matlab code is:</p>
  
  <pre><code>data=read('file');   % read data from a file
  hwin=hanning(L);     % generate hanning window
  hwin=hwin/sum(hwin); % normalize
  data_filtered=conv(data,hwin,'same');  % filtering
  </code></pre>
  
  <p>Now my question is how to set the parameter L to get my required result.  Does L means Full Width at Half Maximum (FWHM)?  What does L mean when applying it to 6-hour interval data?</p>