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author
Daniele Nicolodi <nicolodi@science.unitn.it>
date
Mon, 05 Dec 2011 16:20:06 +0100 (2011-12-05)
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+ − <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">