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<span class="refentrytitle">butterlp</span>
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<p>butterlp —
A low-pass Butterworth filter.
</p>
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<div class="refsect1" title="Description">
<a id="idp15064568"></a>
<h2>Description</h2>
<p>
Implementation of a second-order low-pass Butterworth filter. This opcode can also be written as <a class="link" href="butlp.html" title="butlp"><em class="citetitle">butlp</em></a>.
</p>
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<div class="refsect1" title="Syntax">
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<h2>Syntax</h2>
<pre class="synopsis">ares <span class="command"><strong>butterlp</strong></span> asig, kfreq [, iskip]</pre>
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<div class="refsect1" title="Initialization">
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<h2>Initialization</h2>
<p>
<span class="emphasis"><em>iskip</em></span> (optional, default=0) -- Skip initialization if present and non-zero.
</p>
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<div class="refsect1" title="Performance">
<a id="idp15077280"></a>
<h2>Performance</h2>
<p>
These filters are Butterworth second-order IIR filters. They are slightly slower than the original filters in Csound, but they offer an almost flat passband and very good precision and stopband attenuation.
</p>
<p>
<span class="emphasis"><em>asig</em></span> -- Input signal to be filtered.
</p>
<p>
<span class="emphasis"><em>kfreq</em></span> -- Cutoff or center frequency for each of the filters.
</p>
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<div class="refsect1" title="Examples">
<a id="idp15079376"></a>
<h2>Examples</h2>
<p>
Here is an example of the butterlp opcode. It uses the file <a class="ulink" href="examples/butterlp.csd" target="_top"><em class="citetitle">butterlp.csd</em></a>.
</p>
<div class="example">
<a id="idp15080368"></a>
<p class="title">
<strong>Example 88. Example of the butterlp 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">;;;RT audio out</span>
<span class="comment">;-iadc ;;;uncomment -iadc if RT audio input is needed too</span>
<span class="comment">; For Non-realtime ouput leave only the line below:</span>
<span class="comment">; -o butterlp.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 <span class="comment">; White noise signal</span>
asig <span class="opc">rand</span> 0.5
<span class="opc">outs</span> asig, asig
<span class="oblock">endin</span>
<span class="oblock">instr</span> 2 <span class="comment">; filtered noise</span>
asig <span class="opc">rand</span> 0.7
alp <span class="opc">butterlp</span> asig, 1000 <span class="comment">;cutting frequencies above 1 KHz</span>
<span class="opc">outs</span> alp, alp
<span class="oblock">endin</span>
<span class="csdtag"></CsInstruments></span>
<span class="csdtag"><CsScore></span>
<span class="stamnt">i</span> 1 0 2
<span class="stamnt">i</span> 2 2.5 2
<span class="stamnt">e</span>
<span class="csdtag"></CsScore></span>
<span class="csdtag"></CsoundSynthesizer></span>
</pre>
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<p><br class="example-break" />
</p>
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<div class="refsect1" title="See Also">
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<h2>See Also</h2>
<p>
<a class="link" href="butterbp.html" title="butterbp"><em class="citetitle">butterbp</em></a>,
<a class="link" href="butterbr.html" title="butterbr"><em class="citetitle">butterbr</em></a>,
<a class="link" href="butterhp.html" title="butterhp"><em class="citetitle">butterhp</em></a>
</p>
</div>
<div class="refsect1" title="Credits">
<a id="idp15114944"></a>
<h2>Credits</h2>
<p>
</p>
<table border="0" summary="Simple list" class="simplelist">
<tr>
<td>Author: Paris Smaragdis</td>
</tr>
<tr>
<td>MIT, Cambridge</td>
</tr>
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<td>1995</td>
</tr>
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<p>
</p>
<p>Existed in 3.30</p>
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