Mercurial > hg > ltpda
diff m-toolbox/html_help/help/ug/sigproc_fir.html @ 0:f0afece42f48
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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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/m-toolbox/html_help/help/ug/sigproc_fir.html Wed Nov 23 19:22:13 2011 +0100 @@ -0,0 +1,164 @@ +<!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>FIR Filters (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= + "sigproc_iir.html"><img src="b_prev.gif" border="0" align= + "bottom" alt="IIR Filters"></a> <a href= + "sigproc_filterbanks.html"><img src="b_next.gif" border="0" align= + "bottom" alt="Filter banks"></a></td> + </tr> + </table> + + <h1 class="title"><a name="f3-12899" id="f3-12899"></a>FIR Filters</h1> + <hr> + + <p> + <p> + Finite Impulse Response filters are those filters present a non-zero finite length response + when excited with a very brief (ideally an infinite peak) input signal. A linear causal + FIR filter can be described by the following difference equation +</p> +<div align="center"> + <IMG src="images/sigproc_8.png" width="157" height="56" align="middle" border="0"> +</div> +<p> + This operation describe a nonrecursive system, i.e. a system that only depends on current + and past samples of the input data stream <tt>x[n]</tt> +</p> +<h2><a name="FIRbuild">Creating a FIR filter in the LTPDA</a></h2> +<p> + The LTPDA Toolbox allows the implementation of FIR filters by means of the + <a href="class_desc_mfir.html"> mfir class</a>. +</p> +<h2><a name="FIRplist">Creating from a plist</a></h2> +<p> + The following example creates an order 64 highpass filter with high frequency gain 2. + The filter is designed for 1 Hz sampled data and has a cut-off frequency of 0.2 Hz. +</p> +<div class="fragment"><pre> + + pl = plist(<span class="string">'type'</span>, <span class="string">'highpass'</span>, ... + <span class="string">'order'</span>, 64, ... + <span class="string">'gain'</span>, 2.0, ... + <span class="string">'fs'</span>, 1, ... + <span class="string">'fc'</span>, 0.2); + f = mfir(pl) +</pre></div> + +<h2><a name="FIRdiff">Creating from a difference equation</a></h2> +<p> + The filter can be defined in terms of two vectors specifying the coefficients of the filter + and the sampling frequency. The following example creates a FIR filter with sampling frequency + 1 Hz and the following recursive equation: +</p> + +<div align="center"> +<IMG src="images/sigproc_10.png" width="202" height="28" align="middle" border="0"></div> +</div> + +<p><br></p> + +<div class="fragment"><pre> + + b = [-0.8 10]; + fs = 1; + f = mfir(b,fs) +</pre></div> + +<h2><a name="FIRfromAO">Creating from an Analysis Object</a></h2> +<p> + A FIR filter can be generated based on the magnitude of the input Analysis Object or fsdata object. + In the following example a fsdata object is first generated and then passed to the mfir constructor + to obtain the equivalent FIR filter. +</p> + +<div class="fragment"><pre> + + fs = 10; <span class="comment">% sampling frequency</span> + f = linspace(0, fs/2, 1000); + y = 1./(1+(0.1*2*pi*f).^2); <span class="comment">% an arbitrary function</span> + fsd = fsdata(f,y,fs); <span class="comment">% build the fsdata object</span> + f = mfir(ao(fsd)); + +</pre></div> +<br> +<p> + Available methods for this option are: 'frequency-sampling' (uses fir2), 'least-squares' (uses firls) + and 'Parks-McClellan' (uses firpm) +</p> +<h2><a name="IIRimport">Importing an existing model</a></h2> +<p> + The mfir constructor also accepts as an input existing models in different formats: +</p> +<li> +<li><p>LISO files:<p> + <div class="fragment"><pre> + f = mfir(<span class="string">'foo_fir.fil'</span>) + </pre></div> +</li> +<li><p>XML files:</p> +<div class="fragment"><pre> + f = mfir(<span class="string">'foo_fir.xml'</span>) +</pre></div> +<li><p>MAT files:</p> + <div class="fragment"><pre> + f = mfir(<span class="string">'foo_fir.mat'</span>) + </pre></div> +</li> +<li><p>From repository:</p> + <div class="fragment"><pre> + f = mfir(plist(<span class="string">'hostname'</span>, <span class="string">'localhost'</span>, <span class="string">'database'</span>, <span class="string">'ltpda'</span>, <span class="string">'ID'</span>, [])) + </pre></div> +</li> +</ul> + + </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="sigproc_iir.html"><img src= + "b_prev.gif" border="0" align="bottom" alt= + "IIR Filters"></a> </td> + + <td align="left">IIR Filters</td> + + <td> </td> + + <td align="right">Filter banks</td> + + <td align="right" width="20"><a href= + "sigproc_filterbanks.html"><img src="b_next.gif" border="0" align= + "bottom" alt="Filter banks"></a></td> + </tr> + </table><br> + + <p class="copy">©LTP Team</p> +</body> +</html>