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author Daniele Nicolodi <nicolodi@science.unitn.it>
date Mon, 05 Dec 2011 16:20:06 +0100
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1 <h2>Description</h2>
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2 <p>
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3 Downsampling is the process of reducing the sampling rate of a signal. <a href="matlab:doc('ao/downsample')"><tt>Downsample</tt></a>
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4 reduces the sampling rate of the input AOs by an integer factor by picking up one out of N samples.
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5 Note that no anti-aliasing filter is applied to the original data. Moreover, a <tt>offset</tt> can be
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6 specified, i.e., the sample at which the output data starts ---see examples below.
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7 </p>
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8 <h2>Syntax</h2>
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9 <div class="fragment"><pre>
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10 <br>
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11 b = downsample(a, pl)
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12 </pre>
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13 </div>
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14 <h2>Parameters</h2>
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15 <p> The following parameters can be set in this method:
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16 <ul>
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17 <li> <tt>factor</tt> - decimation factor [by default is 1: no downsampling] (must be an integer) </li>
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18 <li> <tt>offset</tt> - sample offset for decimation </li>
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19 </ul>
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20 </p>
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21 <p>
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22 <h2>Examples</h2>
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23 </p>
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24 <p>
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25 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>.
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26 </p>
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27 <div class="fragment"><pre>
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28 <br>
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29 <span class="comment">% create an AO of random data with fs = 10 Hz</span>
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30 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>);
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31 x = ao(pl)
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32 pl_down = plist(<span class="string">'factor'</span>, 4); <span class="comment">% add the decimation factor</span>
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33 y = downsample(x, pl_down); <span class="comment">% downsample the input AO, x</span>
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34 iplot(x, y)
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35 </pre>
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36 </div>
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37
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38 <img src="images/downsample1.png" alt="Downsample" border="0">
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39
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40 <p>
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41 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.
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42 </p>
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43 <div class="fragment"><pre>
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44 <br>
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45 <span class="comment">% create an AO of random data with fs = 10 Hz</span>
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46 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>);
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47 x = ao(pl)
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48 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>
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49 y = downsample(x, pl_downoff); <span class="comment">% downsample the input AO, x</span>
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50 iplot(x, y)
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51 </pre>
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52 </div>
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53
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54 <img src="images/downsample2.png" alt="Downsample" border="0">