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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">
<a id="idm281472905816056"></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">
<a id="idm281472905745416"></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">
<a id="idm281472905743160"></a>
<h2>Initialization</h2>
<p>
<span class="emphasis"><em>imode</em></span> (optional, default: 0) -- operating mode
</p>
<div class="itemizedlist">
<ul class="itemizedlist" style="list-style-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">
<a id="idm281472905737544"></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">
<a id="idm281472905732776"></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="idm281472905731000"></a>
<p class="title">
<strong>Example 661. 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>
<div class="refsect1">
<a id="idm281472729390312"></a>
<pre class="programlisting">
<span class="nt"><CsoundSynthesizer></span>
<span class="nt"><CsOptions></span>
<span class="c1">; Select audio/midi flags here according to platform</span>
<span class="c1">; Audio out Audio in No messages</span>
-odac -iadc -d <span class="c1">;;;RT audio I/O</span>
<span class="c1">; For Non-realtime ouput leave only the line below:</span>
<span class="c1">; -o pareq.wav -W ;;; for file output any platform</span>
<span class="nt"></CsOptions></span>
<span class="nt"><CsInstruments></span>
<span class="vg">sr</span> <span class="o">=</span> <span class="mi">44100</span>
<span class="vg">kr</span> <span class="o">=</span> <span class="mi">4410</span>
<span class="vg">ksmps</span> <span class="o">=</span> <span class="mi">10</span>
<span class="vg">nchnls</span> <span class="o">=</span> <span class="mi">2</span>
<span class="kd">instr</span> <span class="nf">15</span>
i<span class="n">fc</span> <span class="o">=</span> <span class="nb">p4</span> <span class="c1">; Center / Shelf</span>
k<span class="n">q</span> <span class="o">=</span> <span class="nb">p5</span> <span class="c1">; Quality factor sqrt(.5) is no resonance</span>
k<span class="n">v</span> <span class="o">=</span> <span class="nb">ampdb</span><span class="p">(</span><span class="nb">p6</span><span class="p">)</span> <span class="c1">; Volume Boost/Cut</span>
i<span class="n">mode</span> <span class="o">=</span> <span class="nb">p7</span> <span class="c1">; Mode 0=Peaking EQ, 1=Low Shelf, 2=High Shelf</span>
k<span class="n">fc</span> <span class="nb">linseg</span> i<span class="n">fc</span><span class="o">*</span><span class="mi">2</span><span class="p">,</span> <span class="nb">p3</span><span class="p">,</span> i<span class="n">fc</span><span class="o">/</span><span class="mi">2</span>
a<span class="n">sig</span> <span class="nb">rand</span> <span class="mi">5000</span> <span class="c1">; Random number source for testing</span>
a<span class="n">out</span> <span class="nb">pareq</span> a<span class="n">sig</span><span class="p">,</span> k<span class="n">fc</span><span class="p">,</span> k<span class="n">v</span><span class="p">,</span> k<span class="n">q</span><span class="p">,</span> i<span class="n">mode</span> <span class="c1">; Parmetric equalization</span>
<span class="nb">outs</span> a<span class="n">out</span><span class="p">,</span> a<span class="n">out</span> <span class="c1">; Output the results</span>
<span class="kd">endin</span>
<span class="nt"></CsInstruments></span>
<span class="nt"><CsScore></span>
<span class="c1">; SCORE:</span>
<span class="c1">; Sta Dur Fcenter Q Boost/Cut(dB) Mode</span>
<span class="nb">i</span><span class="mi">15</span> <span class="mi">0</span> <span class="mi">1</span> <span class="mi">10000</span> <span class="mf">.2</span> <span class="mi">12</span> <span class="mi">1</span>
<span class="nb">i</span><span class="mi">15</span> <span class="o">+</span> <span class="o">.</span> <span class="mi">5000</span> <span class="mf">.2</span> <span class="mi">12</span> <span class="mi">1</span>
<span class="nb">i</span><span class="mi">15</span> <span class="o">.</span> <span class="o">.</span> <span class="mi">1000</span> <span class="mf">.707</span> <span class="o">-</span><span class="mi">12</span> <span class="mi">2</span>
<span class="nb">i</span><span class="mi">15</span> <span class="o">.</span> <span class="o">.</span> <span class="mi">5000</span> <span class="mf">.1</span> <span class="o">-</span><span class="mi">12</span> <span class="mi">0</span>
<span class="nb">e</span>
<span class="nt"></CsScore></span>
<span class="nt"></CsoundSynthesizer></span>
</pre>
</div>
</div>
</div>
<p><br class="example-break" />
</p>
</div>
<div class="refsect1">
<a id="idm281472905726776"></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>
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