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  <h1 class="title"><a name="f3-12899" id="f3-12899"></a>Downsampling data</h1>
  <hr>

  <p>
	<h2>Description</h2>
<p>
  Downsampling is the process of reducing the sampling rate of a signal. <a href="matlab:doc('ao/downsample')"><tt>Downsample</tt></a>
  reduces the sampling rate of the input AOs by an integer factor by picking up one out of N samples.
  Note that no anti-aliasing filter is applied to the original data. Moreover, a <tt>offset</tt> can be
  specified, i.e., the sample at which the output data starts ---see examples below.
</p>
<h2>Syntax</h2>
<div class="fragment"><pre>
    <br>
    b = downsample(a, pl)
  </pre>
</div>
<h2>Parameters</h2>
<p>  The following parameters can be set in this method:
  <ul>
    <li> <tt>factor</tt> - decimation factor [by default is 1: no downsampling] (must be an integer) </li>
    <li> <tt>offset</tt> - sample offset for decimation </li>
  </ul>
</p>
<p>
  <h2>Examples</h2>
</p>
<p>
  1. Downsampling a sequence of random data at original sampling rate of 10 Hz by a factor of 4 (<tt>fsout</tt> = 2.5 Hz) and no <tt>offset</tt>.
</p>
<div class="fragment"><pre>
    <br>
    <span class="comment">% create an AO of random data with fs = 10 Hz</span>
    pl      = plist(<span class="string">'tsfcn'</span>, <span class="string">'randn(size(t))'</span>,<span class="string">'fs'</span>,10,<span class="string">'nsecs'</span>,10,<span class="string">'yunits'</span>,<span class="string">'m'</span>);
    x       = ao(pl)
    pl_down = plist(<span class="string">'factor'</span>, 4);     <span class="comment">% add the decimation factor</span>
    y       = downsample(x, pl_down); <span class="comment">% downsample the input AO, x</span>
    iplot(x, y)
  </pre>
</div>

<img src="images/downsample1.png" alt="Downsample" border="0">

<p>
  2. Downsampling a sequence of random data at original sampling rate of 10 Hz by a factor of 4 (<tt>fsout</tt> = 2.5 Hz) and <tt>offset</tt> = 10.
</p>
<div class="fragment"><pre>
    <br>
    <span class="comment">% create an AO of random data with fs = 10 Hz</span>
    pl         = plist(<span class="string">'tsfcn'</span>, <span class="string">'randn(size(t))'</span>,<span class="string">'fs'</span>,10,<span class="string">'nsecs'</span>,10,<span class="string">'yunits'</span>,<span class="string">'m'</span>);
    x          = ao(pl)
    pl_downoff = plist(<span class="string">'factor'</span>, 4,<span class="string">'offset'</span>,10);  <span class="comment">% add the decimation factor and the offset parameter</span>
    y          = downsample(x, pl_downoff);       <span class="comment">% downsample the input AO, x</span>
    iplot(x, y)
  </pre>
</div>

<img src="images/downsample2.png" alt="Downsample" border="0">

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      <td align="right">Upsampling data</td>

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  <p class="copy">&copy;LTP Team</p>
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author	Daniele Nicolodi <nicolodi@science.unitn.it>
date	Wed, 23 Nov 2011 19:22:13 +0100
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