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Move more functions to utils.repository
author Daniele Nicolodi <nicolodi@science.unitn.it>
date Mon, 05 Dec 2011 16:20:06 +0100
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1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
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2 "http://www.w3.org/TR/1999/REC-html401-19991224/loose.dtd">
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3
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4 <html lang="en">
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5 <head>
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6 <meta name="generator" content=
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7 "HTML Tidy for Mac OS X (vers 1st December 2004), see www.w3.org">
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8 <meta http-equiv="Content-Type" content=
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9 "text/html; charset=us-ascii">
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10
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11 <title>Downsampling data (LTPDA Toolbox)</title>
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12 <link rel="stylesheet" href="docstyle.css" type="text/css">
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13 <meta name="generator" content="DocBook XSL Stylesheets V1.52.2">
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14 <meta name="description" content=
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15 "Presents an overview of the features, system requirements, and starting the toolbox.">
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16 </head>
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17
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18 <body>
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19 <a name="top_of_page" id="top_of_page"></a>
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20
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21 <p style="font-size:1px;">&nbsp;</p>
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22
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23 <table class="nav" summary="Navigation aid" border="0" width=
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24 "100%" cellpadding="0" cellspacing="0">
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25 <tr>
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26 <td valign="baseline"><b>LTPDA Toolbox</b></td><td><a href="../helptoc.html">contents</a></td>
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27
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28 <td valign="baseline" align="right"><a href=
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29 "preproc.html"><img src="b_prev.gif" border="0" align=
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30 "bottom" alt="Signal Pre-processing in LTPDA"></a>&nbsp;&nbsp;&nbsp;<a href=
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31 "upsample.html"><img src="b_next.gif" border="0" align=
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32 "bottom" alt="Upsampling data"></a></td>
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33 </tr>
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34 </table>
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35
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36 <h1 class="title"><a name="f3-12899" id="f3-12899"></a>Downsampling data</h1>
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37 <hr>
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38
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39 <p>
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40 <h2>Description</h2>
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41 <p>
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42 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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43 reduces the sampling rate of the input AOs by an integer factor by picking up one out of N samples.
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44 Note that no anti-aliasing filter is applied to the original data. Moreover, a <tt>offset</tt> can be
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45 specified, i.e., the sample at which the output data starts ---see examples below.
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46 </p>
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47 <h2>Syntax</h2>
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48 <div class="fragment"><pre>
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49 <br>
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50 b = downsample(a, pl)
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51 </pre>
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52 </div>
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53 <h2>Parameters</h2>
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54 <p> The following parameters can be set in this method:
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55 <ul>
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56 <li> <tt>factor</tt> - decimation factor [by default is 1: no downsampling] (must be an integer) </li>
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57 <li> <tt>offset</tt> - sample offset for decimation </li>
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58 </ul>
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59 </p>
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60 <p>
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61 <h2>Examples</h2>
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62 </p>
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63 <p>
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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>.
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65 </p>
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66 <div class="fragment"><pre>
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67 <br>
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68 <span class="comment">% create an AO of random data with fs = 10 Hz</span>
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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>);
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70 x = ao(pl)
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71 pl_down = plist(<span class="string">'factor'</span>, 4); <span class="comment">% add the decimation factor</span>
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72 y = downsample(x, pl_down); <span class="comment">% downsample the input AO, x</span>
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73 iplot(x, y)
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74 </pre>
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75 </div>
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76
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77 <img src="images/downsample1.png" alt="Downsample" border="0">
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78
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79 <p>
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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.
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81 </p>
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82 <div class="fragment"><pre>
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83 <br>
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84 <span class="comment">% create an AO of random data with fs = 10 Hz</span>
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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>);
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86 x = ao(pl)
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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>
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88 y = downsample(x, pl_downoff); <span class="comment">% downsample the input AO, x</span>
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89 iplot(x, y)
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90 </pre>
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91 </div>
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92
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93 <img src="images/downsample2.png" alt="Downsample" border="0">
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94
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95 </p>
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96
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97 <br>
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98 <br>
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99 <table class="nav" summary="Navigation aid" border="0" width=
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100 "100%" cellpadding="0" cellspacing="0">
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101 <tr valign="top">
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102 <td align="left" width="20"><a href="preproc.html"><img src=
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103 "b_prev.gif" border="0" align="bottom" alt=
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104 "Signal Pre-processing in LTPDA"></a>&nbsp;</td>
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105
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106 <td align="left">Signal Pre-processing in LTPDA</td>
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107
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108 <td>&nbsp;</td>
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109
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110 <td align="right">Upsampling data</td>
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111
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112 <td align="right" width="20"><a href=
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113 "upsample.html"><img src="b_next.gif" border="0" align=
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114 "bottom" alt="Upsampling data"></a></td>
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115 </tr>
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116 </table><br>
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117
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118 <p class="copy">&copy;LTP Team</p>
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119 </body>
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120 </html>