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