165 lines
5.7 KiB
HTML
165 lines
5.7 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<!--Converted with LaTeX2HTML 2002-2-1 (1.71)
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original version by: Nikos Drakos, CBLU, University of Leeds
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* revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan
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* with significant contributions from:
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Jens Lippmann, Marek Rouchal, Martin Wilck and others -->
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<HTML>
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<HEAD>
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<TITLE>Equalizing filters</TITLE>
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<META NAME="description" CONTENT="Equalizing filters">
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<BR>
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<B> Next:</B> <A NAME="tex2html2534"
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HREF="node132.html">Elementary filters</A>
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<B> Up:</B> <A NAME="tex2html2528"
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HREF="node128.html">Taxonomy of filters</A>
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<B> Previous:</B> <A NAME="tex2html2524"
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HREF="node130.html">Band-pass and stop-band filters</A>
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<B> <A NAME="tex2html2530"
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HREF="node4.html">Contents</A></B>
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<B> <A NAME="tex2html2532"
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HREF="node201.html">Index</A></B>
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<BR>
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<BR>
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<!--End of Navigation Panel-->
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<H2><A NAME="SECTION001213000000000000000"></A>
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<A NAME="sect8.equalizing"></A>
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<BR>
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Equalizing filters
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</H2>
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<P>
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In some applications, such as
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<A NAME="10107"></A><I>equalization</I>,
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the goal isn't to pass signals of certain frequencies while stopping others
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altogether, but to make controllable adjustments, boosting or attenuating
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a signal, over a frequency range, by a desired gain. Two filter types
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are useful for this. First, a
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<A NAME="10109"></A><A NAME="10110"></A><I>shelving filter</I>
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(Figure <A HREF="#fig08.05">8.5</A>) is used for selectively boosting or reducing either the
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low or high end of the frequency range. Below a selectable crossover frequency,
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the filter tends toward a low-frequency gain, and above it it tends toward a
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different, high-frequency one. The crossover frequency, low-frequency gain,
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and high-frequency gain can all be adjusted independently.
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<P>
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<DIV ALIGN="CENTER"><A NAME="fig08.05"></A><A NAME="10115"></A>
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<TABLE>
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<CAPTION ALIGN="BOTTOM"><STRONG>Figure 8.5:</STRONG>
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A shelving filter, showing low and high frequency gain, and
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crossover frequency.</CAPTION>
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<TR><TD><IMG
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WIDTH="312" HEIGHT="211" BORDER="0"
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SRC="img858.png"
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ALT="\begin{figure}\psfig{file=figs/fig08.05.ps}\end{figure}"></TD></TR>
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</TABLE>
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</DIV>
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<P>
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Second, a
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<A NAME="10118"></A><A NAME="10119"></A><I>peaking filter</I>
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(Figure <A HREF="#fig08.06">8.6</A>) is capable of boosting or attenuating signals within
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a range of frequencies. The center frequency and bandwidth (which together
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control the range of frequencies affected), and the in-band and out-of-band
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gains are separately adjustible.
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<P>
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<DIV ALIGN="CENTER"><A NAME="fig08.06"></A><A NAME="10124"></A>
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<TABLE>
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<CAPTION ALIGN="BOTTOM"><STRONG>Figure 8.6:</STRONG>
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A peaking filter, with controllable center frequency, bandwidth,
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and in-band and out-of-band gains.</CAPTION>
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<TR><TD><IMG
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WIDTH="290" HEIGHT="243" BORDER="0"
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SRC="img859.png"
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ALT="\begin{figure}\psfig{file=figs/fig08.06.ps}\end{figure}"></TD></TR>
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</TABLE>
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</DIV>
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<P>
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Parametric equalizers often employ two shelving filters (one each to adjust
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the low and high ends of the spectrum) and two or three peaking filters to
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adjust bands in between.
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<P>
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<B> Next:</B> <A NAME="tex2html2534"
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HREF="node132.html">Elementary filters</A>
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<B> Up:</B> <A NAME="tex2html2528"
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HREF="node128.html">Taxonomy of filters</A>
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<B> Previous:</B> <A NAME="tex2html2524"
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HREF="node130.html">Band-pass and stop-band filters</A>
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<B> <A NAME="tex2html2530"
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HREF="node4.html">Contents</A></B>
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<B> <A NAME="tex2html2532"
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HREF="node201.html">Index</A></B>
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<!--End of Navigation Panel-->
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<ADDRESS>
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Miller Puckette
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2006-12-30
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</ADDRESS>
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