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author Daniele Nicolodi <nicolodi@science.unitn.it>
date Wed, 23 Nov 2011 19:22:13 +0100
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11 <title>Downsampling data (LTPDA Toolbox)</title>
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21 <p style="font-size:1px;">&nbsp;</p>
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23 <table class="nav" summary="Navigation aid" border="0" width=
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26 <td valign="baseline"><b>LTPDA Toolbox</b></td><td><a href="../helptoc.html">contents</a></td>
27
28 <td valign="baseline" align="right"><a href=
29 "preproc.html"><img src="b_prev.gif" border="0" align=
30 "bottom" alt="Signal Pre-processing in LTPDA"></a>&nbsp;&nbsp;&nbsp;<a href=
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32 "bottom" alt="Upsampling data"></a></td>
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34 </table>
35
36 <h1 class="title"><a name="f3-12899" id="f3-12899"></a>Downsampling data</h1>
37 <hr>
38
39 <p>
40 <h2>Description</h2>
41 <p>
42 Downsampling is the process of reducing the sampling rate of a signal. <a href="matlab:doc('ao/downsample')"><tt>Downsample</tt></a>
43 reduces the sampling rate of the input AOs by an integer factor by picking up one out of N samples.
44 Note that no anti-aliasing filter is applied to the original data. Moreover, a <tt>offset</tt> can be
45 specified, i.e., the sample at which the output data starts ---see examples below.
46 </p>
47 <h2>Syntax</h2>
48 <div class="fragment"><pre>
49 <br>
50 b = downsample(a, pl)
51 </pre>
52 </div>
53 <h2>Parameters</h2>
54 <p> The following parameters can be set in this method:
55 <ul>
56 <li> <tt>factor</tt> - decimation factor [by default is 1: no downsampling] (must be an integer) </li>
57 <li> <tt>offset</tt> - sample offset for decimation </li>
58 </ul>
59 </p>
60 <p>
61 <h2>Examples</h2>
62 </p>
63 <p>
64 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>.
65 </p>
66 <div class="fragment"><pre>
67 <br>
68 <span class="comment">% create an AO of random data with fs = 10 Hz</span>
69 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>);
70 x = ao(pl)
71 pl_down = plist(<span class="string">'factor'</span>, 4); <span class="comment">% add the decimation factor</span>
72 y = downsample(x, pl_down); <span class="comment">% downsample the input AO, x</span>
73 iplot(x, y)
74 </pre>
75 </div>
76
77 <img src="images/downsample1.png" alt="Downsample" border="0">
78
79 <p>
80 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.
81 </p>
82 <div class="fragment"><pre>
83 <br>
84 <span class="comment">% create an AO of random data with fs = 10 Hz</span>
85 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>);
86 x = ao(pl)
87 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>
88 y = downsample(x, pl_downoff); <span class="comment">% downsample the input AO, x</span>
89 iplot(x, y)
90 </pre>
91 </div>
92
93 <img src="images/downsample2.png" alt="Downsample" border="0">
94
95 </p>
96
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102 <td align="left" width="20"><a href="preproc.html"><img src=
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106 <td align="left">Signal Pre-processing in LTPDA</td>
107
108 <td>&nbsp;</td>
109
110 <td align="right">Upsampling data</td>
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