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<div class="refentry" title="eqfil">
<a id="eqfil"></a>
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<h2>
<span class="refentrytitle">eqfil</span>
</h2>
<p>eqfil —
Equalizer filter
</p>
</div>
<div class="refsect1" title="Description">
<a id="idp19355056"></a>
<h2>Description</h2>
<p>
The opcode eqfil is a 2nd order tunable equalisation filter based on Regalia and Mitra
design ("Tunable Digital Frequency Response Equalization Filters", IEEE Trans.
on Ac., Sp. and Sig Proc., 35 (1), 1987). It provides a peak/notch filter for
building parametric/graphic equalisers.
</p>
<p>
The amplitude response for this filter will be flat (=1) for <span class="emphasis"><em>kgain</em></span>=1. With <span class="emphasis"><em>kgain</em></span> bigger than 1, there
will be a peak at the centre frequency, whose width is given by the <span class="emphasis"><em>kbw</em></span> parameter, but
outside this band, the response will tend towards 1. Conversely, if <span class="emphasis"><em>kgain</em></span> is smaller than 1, a notch will
be created around the CF.
</p>
</div>
<div class="refsect1" title="Syntax">
<a id="idp19376008"></a>
<h2>Syntax</h2>
<pre class="synopsis">asig <span class="command"><strong>eqfil</strong></span> ain, kcf, kbw, kgain[, istor]</pre>
</div>
<div class="refsect1" title="Initialization">
<a id="idp19377104"></a>
<h2>Initialization</h2>
<p>
<span class="emphasis"><em>istor</em></span> --initial disposition of internal data space. Since
filtering incorporates a feedback loop of previous output,
the initial status of the storage space used is significant.
A zero value will clear the space; a non-zero value will allow
previous information to remain. The default value is 0.
</p>
</div>
<div class="refsect1" title="Performance">
<a id="idp19378256"></a>
<h2>Performance</h2>
<p>
<span class="emphasis"><em>asig</em></span> -- filtered output signal.
</p>
<p>
<span class="emphasis"><em>ain</em></span> -- input signal.
</p>
<p>
<span class="emphasis"><em>kcf</em></span> -- filter centre frequency.
</p>
<p>
<span class="emphasis"><em>kbw</em></span> -- peak/notch bandwidth (Hz).
</p>
<p>
<span class="emphasis"><em>kgain</em></span> -- peak/notch gain.
</p>
</div>
<div class="refsect1" title="Examples">
<a id="idp19397784"></a>
<h2>Examples</h2>
<p>
Here is an example of the eqfil opcode. It uses the file <a class="ulink" href="examples/eqfil.csd" target="_top"><em class="citetitle">eqfil.csd</em></a>.
</p>
<div class="example">
<a id="idp19398680"></a>
<p class="title">
<strong>Example 208. Example of the eqfil 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>
-odac <span class="comment">;;;realtime audio out</span>
<span class="comment">;-iadc ;;;uncomment -iadc if realtime audio input is needed too</span>
<span class="comment">; For Non-realtime ouput leave only the line below:</span>
<span class="comment">; -o eqfil.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">ksmps</span> <span class="op">=</span> 32
<span class="ohdr">nchnls</span> <span class="op">=</span> 2
<span class="ohdr">0dbfs</span> <span class="op">=</span> 1
<span class="oblock">instr</span> 1
kcf <span class="op">=</span> p4
kfe <span class="opc">expseg</span> 10, p3<span class="op">*</span>0.9, 1800, p3<span class="op">*</span>0.1, 175
kenv <span class="opc">linen</span> .03, 0.05, p3, 0.05 <span class="comment">;low amplitude is needed to avoid clipping</span>
asig <span class="opc">buzz</span> kenv, kfe, <span class="ohdr">sr</span><span class="op">/</span>(2<span class="op">*</span>kfe), 1
afil <span class="opc">eqfil</span> asig, kcf, 200, 10
<span class="opc">outs</span> afil<span class="op">*</span>20, afil<span class="op">*</span>20
<span class="oblock">endin</span>
<span class="csdtag"></CsInstruments></span>
<span class="csdtag"><CsScore></span>
<span class="comment">; a sine wave.</span>
<span class="stamnt">f</span> 1 0 16384 10 1
<span class="stamnt">i</span> 1 0 10 200 <span class="comment">;filter centre freq=200</span>
<span class="stamnt">i</span> 1 + 10 1500 <span class="comment">;filter centre freq=1500</span>
<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="idp19400568"></a>
<h2>Credits</h2>
<p>
</p>
<table border="0" summary="Simple list" class="simplelist">
<tr>
<td>Author: Victor Lazzarini</td>
</tr>
<tr>
<td>April 2007</td>
</tr>
</table>
<p>
</p>
<p>New in version 5.06</p>
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