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author | Daniele Nicolodi <nicolodi@science.unitn.it> |
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date | Mon, 05 Dec 2011 16:20:06 +0100 |
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/1999/REC-html401-19991224/loose.dtd"> <html lang="en"> <head> <meta name="generator" content= "HTML Tidy for Mac OS X (vers 1st December 2004), see www.w3.org"> <meta http-equiv="Content-Type" content= "text/html; charset=us-ascii"> <title>Downsampling data (LTPDA Toolbox)</title> <link rel="stylesheet" href="docstyle.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.52.2"> <meta name="description" content= "Presents an overview of the features, system requirements, and starting the toolbox."> </head> <body> <a name="top_of_page" id="top_of_page"></a> <p style="font-size:1px;"> </p> <table class="nav" summary="Navigation aid" border="0" width= "100%" cellpadding="0" cellspacing="0"> <tr> <td valign="baseline"><b>LTPDA Toolbox</b></td><td><a href="../helptoc.html">contents</a></td> <td valign="baseline" align="right"><a href= "preproc.html"><img src="b_prev.gif" border="0" align= "bottom" alt="Signal Pre-processing in LTPDA"></a> <a href= "upsample.html"><img src="b_next.gif" border="0" align= "bottom" alt="Upsampling data"></a></td> </tr> </table> <h1 class="title"><a name="f3-12899" id="f3-12899"></a>Downsampling data</h1> <hr> <p> <h2>Description</h2> <p> Downsampling is the process of reducing the sampling rate of a signal. <a href="matlab:doc('ao/downsample')"><tt>Downsample</tt></a> reduces the sampling rate of the input AOs by an integer factor by picking up one out of N samples. Note that no anti-aliasing filter is applied to the original data. Moreover, a <tt>offset</tt> can be specified, i.e., the sample at which the output data starts ---see examples below. </p> <h2>Syntax</h2> <div class="fragment"><pre> <br> b = downsample(a, pl) </pre> </div> <h2>Parameters</h2> <p> The following parameters can be set in this method: <ul> <li> <tt>factor</tt> - decimation factor [by default is 1: no downsampling] (must be an integer) </li> <li> <tt>offset</tt> - sample offset for decimation </li> </ul> </p> <p> <h2>Examples</h2> </p> <p> 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>. </p> <div class="fragment"><pre> <br> <span class="comment">% create an AO of random data with fs = 10 Hz</span> 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>); x = ao(pl) pl_down = plist(<span class="string">'factor'</span>, 4); <span class="comment">% add the decimation factor</span> y = downsample(x, pl_down); <span class="comment">% downsample the input AO, x</span> iplot(x, y) </pre> </div> <img src="images/downsample1.png" alt="Downsample" border="0"> <p> 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. </p> <div class="fragment"><pre> <br> <span class="comment">% create an AO of random data with fs = 10 Hz</span> 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>); x = ao(pl) 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> y = downsample(x, pl_downoff); <span class="comment">% downsample the input AO, x</span> iplot(x, y) </pre> </div> <img src="images/downsample2.png" alt="Downsample" border="0"> </p> <br> <br> <table class="nav" summary="Navigation aid" border="0" width= "100%" cellpadding="0" cellspacing="0"> <tr valign="top"> <td align="left" width="20"><a href="preproc.html"><img src= "b_prev.gif" border="0" align="bottom" alt= "Signal Pre-processing in LTPDA"></a> </td> <td align="left">Signal Pre-processing in LTPDA</td> <td> </td> <td align="right">Upsampling data</td> <td align="right" width="20"><a href= "upsample.html"><img src="b_next.gif" border="0" align= "bottom" alt="Upsampling data"></a></td> </tr> </table><br> <p class="copy">©LTP Team</p> </body> </html>