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<div class="refentry" title="pareq">
<a id="pareq"></a>
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<h2>
<span class="refentrytitle">pareq</span>
</h2>
<p>pareq —
Implementation of Zoelzer's parametric equalizer filters.
</p>
</div>
<div class="refsect1" title="Description">
<a id="idp35237120"></a>
<h2>Description</h2>
<p>
Implementation of Zoelzer's parametric equalizer filters, with some modifications by the author.
</p>
<p>
The formula for the low shelf filter is:
</p>
<div class="literallayout">
<p><br />
omega = 2*pi*f/sr<br />
K = tan(omega/2)<br />
<br />
b0 = 1 + sqrt(2*V)*K + V*K^2<br />
b1 = 2*(V*K^2 - 1)<br />
b2 = 1 - sqrt(2*V)*K + V*K^2<br />
<br />
a0 = 1 + K/Q + K^2<br />
a1 = 2*(K^2 - 1)<br />
a2 = 1 - K/Q + K^2<br />
</p>
</div>
<p>
</p>
<p>
The formula for the high shelf filter is:
</p>
<div class="literallayout">
<p><br />
omega = 2*pi*f/sr<br />
K = tan((pi-omega)/2)<br />
<br />
b0 = 1 + sqrt(2*V)*K + V*K^2<br />
b1 = -2*(V*K^2 - 1)<br />
b1 = 1 - sqrt(2*V)*K + V*K^2<br />
<br />
a0 = 1 + K/Q + K^2<br />
a1 = -2*(K^2 - 1)<br />
a2 = 1 - K/Q + K^2<br />
</p>
</div>
<p>
</p>
<p>
The formula for the peaking filter is:
</p>
<div class="literallayout">
<p><br />
omega = 2*pi*f/sr<br />
K = tan(omega/2)<br />
<br />
b0 = 1 + V*K/2 + K^2<br />
b1 = 2*(K^2 - 1)<br />
b2 = 1 - V*K/2 + K^2<br />
<br />
a0 = 1 + K/Q + K^2<br />
a1 = 2*(K^2 - 1)<br />
a2 = 1 - K/Q + K^2<br />
</p>
</div>
<p>
</p>
</div>
<div class="refsect1" title="Syntax">
<a id="idp35250128"></a>
<h2>Syntax</h2>
<pre class="synopsis">ares <span class="command"><strong>pareq</strong></span> asig, kc, kv, kq [, imode] [, iskip]</pre>
</div>
<div class="refsect1" title="Initialization">
<a id="idp35251288"></a>
<h2>Initialization</h2>
<p>
<span class="emphasis"><em>imode</em></span> (optional, default: 0) -- operating mode
</p>
<div class="itemizedlist">
<ul class="itemizedlist" type="disc">
<li class="listitem">
<p>0 = Peaking</p>
</li>
<li class="listitem">
<p>1 = Low Shelving</p>
</li>
<li class="listitem">
<p>2 = High Shelving</p>
</li>
</ul>
</div>
<p>
</p>
<p>
<span class="emphasis"><em>iskip</em></span> (optional, default=0) -- if non zero
skip the initialisation of the filter. (New in Csound version
4.23f13 and 5.0)
</p>
</div>
<div class="refsect1" title="Performance">
<a id="idp35337184"></a>
<h2>Performance</h2>
<p>
<span class="emphasis"><em>kc</em></span> -- center frequency in peaking mode, corner frequency in shelving mode.
</p>
<p>
<span class="emphasis"><em>kv</em></span> -- amount of boost or cut. A value less than 1 is a cut. A value greater than 1 is a boost. A value of 1 is a flat response.
</p>
<p>
<span class="emphasis"><em>kq</em></span> -- Q of the filter (sqrt(.5) is no resonance)
</p>
<p>
<span class="emphasis"><em>asig</em></span> -- the incoming signal
</p>
</div>
<div class="refsect1" title="Examples">
<a id="idp35339808"></a>
<h2>Examples</h2>
<p>
Here is an example of the pareq opcode. It uses the file <a class="ulink" href="examples/pareq.csd" target="_top"><em class="citetitle">pareq.csd</em></a>.
</p>
<div class="example">
<a id="idp35340728"></a>
<p class="title">
<strong>Example 565. Example of the pareq opcode.</strong>
</p>
<div class="example-contents">
<p>See the sections <a class="link" href="UsingRealTime.html" title="Real-Time Audio"><em class="citetitle">Real-time Audio</em></a> and <a class="link" href="CommandFlags.html" title="Csound command line"><em class="citetitle">Command Line Flags</em></a> for more information on using command line flags.</p>
<pre class="programlisting">
<span class="csdtag"><CsoundSynthesizer></span>
<span class="csdtag"><CsOptions></span>
<span class="comment">; Select audio/midi flags here according to platform</span>
<span class="comment">; Audio out Audio in No messages</span>
-odac -iadc -d <span class="comment">;;;RT audio I/O</span>
<span class="comment">; For Non-realtime ouput leave only the line below:</span>
<span class="comment">; -o pareq.wav -W ;;; for file output any platform</span>
<span class="csdtag"></CsOptions></span>
<span class="csdtag"><CsInstruments></span>
<span class="ohdr">sr</span> <span class="op">=</span> 44100
<span class="ohdr">kr</span> <span class="op">=</span> 4410
<span class="ohdr">ksmps</span> <span class="op">=</span> 10
<span class="ohdr">nchnls</span> <span class="op">=</span> 2
<span class="oblock">instr</span> 15
ifc <span class="op">=</span> p4 <span class="comment">; Center / Shelf</span>
kq <span class="op">=</span> p5 <span class="comment">; Quality factor sqrt(.5) is no resonance</span>
kv <span class="op">=</span> <span class="opc">ampdb</span>(p6) <span class="comment">; Volume Boost/Cut</span>
imode <span class="op">=</span> p7 <span class="comment">; Mode 0=Peaking EQ, 1=Low Shelf, 2=High Shelf</span>
kfc <span class="opc">linseg</span> ifc<span class="op">*</span>2, p3, ifc<span class="op">/</span>2
asig <span class="opc">rand</span> 5000 <span class="comment">; Random number source for testing</span>
aout <span class="opc">pareq</span> asig, kfc, kv, kq, imode <span class="comment">; Parmetric equalization</span>
<span class="opc">outs</span> aout, aout <span class="comment">; Output the results</span>
<span class="oblock">endin</span>
<span class="csdtag"></CsInstruments></span>
<span class="csdtag"><CsScore></span>
<span class="comment">; SCORE:</span>
<span class="comment">; Sta Dur Fcenter Q Boost/Cut(dB) Mode</span>
<span class="stamnt">i</span>15 0 1 10000 .2 12 1
<span class="stamnt">i</span>15 + . 5000 .2 12 1
<span class="stamnt">i</span>15 . . 1000 .707 -12 2
<span class="stamnt">i</span>15 . . 5000 .1 -12 0
<span class="stamnt">e</span>
<span class="csdtag"></CsScore></span>
<span class="csdtag"></CsoundSynthesizer></span>
</pre>
</div>
</div>
<p><br class="example-break" />
</p>
</div>
<div class="refsect1" title="Credits">
<a id="idp35343032"></a>
<h2>Credits</h2>
<p>
</p>
<table border="0" summary="Simple list" class="simplelist">
<tr>
<td>Hans Mikelson</td>
</tr>
<tr>
<td>December 1998</td>
</tr>
</table>
<p>
</p>
<p>New in Csound version 3.50</p>
</div>
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