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author Daniele Nicolodi <nicolodi@science.unitn.it>
date Wed, 23 Nov 2011 19:22:13 +0100
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1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
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11 <title>Downsampling a time-series AO (LTPDA Toolbox)</title>
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15 "Presents an overview of the features, system requirements, and starting the toolbox.">
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17
18 <body>
19 <a name="top_of_page" id="top_of_page"></a>
20
21 <p style="font-size:1px;">&nbsp;</p>
22
23 <table class="nav" summary="Navigation aid" border="0" width=
24 "100%" cellpadding="0" cellspacing="0">
25 <tr>
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 "ltpda_training_topic_2.html"><img src="b_prev.gif" border="0" align=
30 "bottom" alt="Topic 2 - Pre-processing of data"></a>&nbsp;&nbsp;&nbsp;<a href=
31 "ltpda_training_topic_2_2.html"><img src="b_next.gif" border="0" align=
32 "bottom" alt="Upsampling a time-series AO"></a></td>
33 </tr>
34 </table>
35
36 <h1 class="title"><a name="f3-12899" id="f3-12899"></a>Downsampling a time-series AO</h1>
37 <hr>
38
39 <p>
40
41 Downsampling reduces the sampling rate of the input AOs by an integer factor, which can be very useful for example to reduce data load.
42
43 <p>The <tt>downsample</tt> method takes the following parameters:
44 <table cellspacing="0" class="body" cellpadding="2" border="0" width="80%">
45 <colgroup>
46 <col width="25%"/>
47 <col width="75%"/>
48 </colgroup>
49 <thead>
50 <tr valign="top">
51 <th class="categorylist">Key</th>
52 <th class="categorylist">Description</th>
53 </tr>
54 </thead>
55 <tbody>
56 <!-- Key 'factor' -->
57 <tr valign="top">
58 <td bgcolor="#f3f4f5">
59 <p><tt>FACTOR</tt></p>
60 </td>
61 <td bgcolor="#f3f4f5">
62 <p>The decimation factor [by default is 1: no downsampling] (must be an integer)</p>
63 </td>
64 </tr>
65 <!-- Key 'offset' -->
66 <tr valign="top">
67 <td bgcolor="#f3f4f5">
68 <p><tt>OFFSET</tt></p>
69 </td>
70 <td bgcolor="#f3f4f5">
71 <p>The sample offset for where the downsampling starts counting. By default, this value is
72 zero so it starts counting from the first sample.</p>
73 </td>
74 </tr>
75 </tbody>
76 </table>
77 </p>
78 <h2><a name="example1">Example 1</h2>
79 <p>
80 First we'll create a time-series of random white noise at 10Hz. To do that,
81 define a <tt>plist</tt> with the key/value pairs shown below, and pass these
82 to the <tt>ao</tt> constructor. If you're using the workbench, add an <tt>ao</tt>
83 constructor block to the canvas and select the parameter set "From Time-series Function" and
84 set the parameters as they are in the <tt>plist</tt> below.
85 </p>
86 <div class="fragment"><pre>
87 <span class="comment">% create an AO of random data with fs = 10 Hz;</span>
88 pl = plist(<span class="string">'name'</span>, <span class="string">'None'</span>, ...
89 <span class="string">'tsfcn'</span>, <span class="string">'randn(size(t))'</span>, <span class="keyword">...</span>
90 <span class="string">'fs'</span>, 10, <span class="keyword">...</span>
91 <span class="string">'yunits'</span>, <span class="string">'m'</span>, <span class="keyword">...</span>
92 <span class="string">'nsecs'</span>, 10);
93 x = ao(pl); <span class="comment">% create AO</span>
94 </pre>
95 </div>
96 <p>
97 Now we will downsample this data by a factor 5 to 2Hz. We use the method <tt>ao/downsample</tt> and set
98 the downsample factor in the <tt>plist</tt> as shown below.
99 </p>
100 <div class="fragment"><pre>
101 pl_down = plist(<span class="string">'factor'</span>, 5); <span class="comment">% add the decimation factor</span>
102 x_down = downsample(x, pl_down); <span class="comment">% downsample the input AO, x</span>
103 iplot(x, x_down) <span class="comment">% plot original,x, and decimated,x_down, AOs</span>
104 </pre>
105 </div>
106 <img src="images/ltpda_training_1/topic2/down1.png" alt="Downsample" border="3">
107 <br>
108 <br>
109 <h2><a name="example2">Example 2</h2>
110 <p>
111 The <tt>downsample</tt> method takes an 'offset' key which controls where the counting starts. The default is
112 to output every Nth sample starting with the first. The 'offset' key tells <tt>downsample</tt> to start the counting
113 from a sample other than the first. The example
114 below outputs every 4th sample starting from sample 10.
115 </p>
116 <div class="fragment"><pre>
117 pl_downoff = plist(<span class="string">'factor'</span>, 4,<span class="string">'offset'</span>,10); <span class="comment">% add decimation factor and offset parameter</span>
118 x_downoff = downsample(x, pl_downoff); <span class="comment">% downsample the input AO, x</span>
119 iplot(x, x_downoff) <span class="comment">% plot original,x, and decimated,x_downoff, AOs</span>
120 </pre>
121 </div>
122 <img src="images/ltpda_training_1/topic2/down2.png" alt="Downsample" border="3">
123
124
125
126 </p>
127
128 <br>
129 <br>
130 <table class="nav" summary="Navigation aid" border="0" width=
131 "100%" cellpadding="0" cellspacing="0">
132 <tr valign="top">
133 <td align="left" width="20"><a href="ltpda_training_topic_2.html"><img src=
134 "b_prev.gif" border="0" align="bottom" alt=
135 "Topic 2 - Pre-processing of data"></a>&nbsp;</td>
136
137 <td align="left">Topic 2 - Pre-processing of data</td>
138
139 <td>&nbsp;</td>
140
141 <td align="right">Upsampling a time-series AO</td>
142
143 <td align="right" width="20"><a href=
144 "ltpda_training_topic_2_2.html"><img src="b_next.gif" border="0" align=
145 "bottom" alt="Upsampling a time-series AO"></a></td>
146 </tr>
147 </table><br>
148
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