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author Daniele Nicolodi <nicolodi@science.unitn.it>
date Wed, 23 Nov 2011 19:22:13 +0100
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  <title>Resampling a time-series AO (LTPDA Toolbox)</title>
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  <h1 class="title"><a name="f3-12899" id="f3-12899"></a>Resampling a time-series AO</h1>
  <hr>
  
  <p>
	<p>
  Resampling is the process of changing the sampling rate of data. The method <tt>ao/resample</tt></a>
  changes the sampling rate of the input AOs to the desired output sampling frequency by performing band-limited
  interpolation, or interpolation.
</p>
<p>
  If the ratio of the input and the desired output sample rate can be expressed as an integer ratio P/Q where both
  P and Q then band-limited interpolation can be performed. In this case, the data-series
  is upsampled (by inserting zeros) and then a low-pass filter is applied at the
  original Nyquist frequency.
</p>
<p>
   The <tt>ao/resample</tt></a> method can be called with the syntax:
</p>
<div class="fragment"><pre>
    b = resample(a, pl)
  </pre>
</div>
<p>
  and can accept the following parameters:
  <table cellspacing="0" class="body" cellpadding="2" border="0" width="80%">
    <colgroup>
      <col width="25%"/>
      <col width="75%"/>
    </colgroup>
    <thead>
      <tr valign="top">
        <th class="categorylist">Key</th>
        <th class="categorylist">Description</th>
      </tr>
    </thead>
    <tbody>
      <!-- Key 'N' -->
      <tr valign="top">
        <td bgcolor="#f3f4f5">
          <p><tt>FSOUT</tt></p>
        </td>
        <td bgcolor="#f3f4f5">
          <p>The desired output frequency (must be positive and integer)</p>
        </td>
      </tr>
      <!-- Key 'FILTER' -->
      <tr valign="top">
        <td bgcolor="#f3f4f5">
          <p><tt>FILTER</tt></p>
        </td>
        <td bgcolor="#f3f4f5">
          <p>The filter to apply in the resampling process</p>
        </td>
      </tr>
    </tbody>
  </table>
</p>
<h2>Example 1</h2>
<p>
  Here we will resample a sequence of random data from the original sampling rate of 1 Hz to
  an output sampling of 50 Hz.
</p>
<div class="fragment"><pre>
    pl    = plist(<span class="string">'name'</span>, <span class="string">'None'</span>, <span class="string">'tsfcn'</span>, <span class="string">'randn(size(t))'</span>,<span class="string">'nsecs'</span>,100,<span class="string">'fs'</span>,1,<span class="string">'yunits'</span>,<span class="string">'m'</span>);
    x     = ao(pl)
    pl_re = plist(<span class="string">'fsout'</span>, 50);
    x_re  = resample(x, pl_re); <span class="comment">% resample the input AO (x) to obtain the resampled output AO (y)</span>
    iplot(x, x_re, plist(<span class="string">'XRanges'</span>, [10 20], ...
                         <span class="string">'Markers'</span>, {<span class="string">'o'</span>, <span class="string">'.'</span>}, ...
                         <span class="string">'LineStyles'</span>, {<span class="string">'-'</span>, <span class="string">'none'</span>})) <span class="comment">% plot original and resampled data</span>
  </pre>
</div>

<img src="images/ltpda_training_1/topic2/re1.png" alt="Resample" border="3">





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