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<h2>
<span class="refentrytitle">butterbp</span>
</h2>
<p>butterbp —
A band-pass Butterworth filter.
</p>
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<div class="refsect1">
<a id="idm281472948694696"></a>
<h2>Description</h2>
<p>
Implementation of a second-order band-pass Butterworth filter. This opcode can also be written as <a class="link" href="butbp.html" title="butbp"><em class="citetitle">butbp</em></a>.
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<h2>Syntax</h2>
<pre class="synopsis">ares <span class="command"><strong>butterbp</strong></span> asig, xfreq, xband [, iskip]</pre>
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<div class="refsect1">
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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">
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<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>xfreq</em></span> -- Cutoff or center frequency for each of the filters.
</p>
<p>
<span class="emphasis"><em>xband</em></span> -- Bandwidth of the bandpass and bandreject filters.
</p>
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<div class="refsect1">
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<h2>Examples</h2>
<p>
Here is an example of the butterbp opcode. It uses the file <a class="ulink" href="examples/butterbp.csd" target="_top"><em class="citetitle">butterbp.csd</em></a>.
</p>
<div class="example">
<a id="idm281472948628488"></a>
<p class="title">
<strong>Example 98. Example of the butterbp 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="idm281472782947464"></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>
-odac <span class="c1">;;;RT audio out</span>
<span class="c1">;-iadc ;;;uncomment -iadc if RT audio input is needed too</span>
<span class="c1">; For Non-realtime ouput leave only the line below:</span>
<span class="c1">; -o butterbp.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">ksmps</span> <span class="o">=</span> <span class="mi">32</span>
<span class="vg">nchnls</span> <span class="o">=</span> <span class="mi">2</span>
<span class="vg">0dbfs</span> <span class="o">=</span> <span class="mi">1</span>
<span class="kd">instr</span> <span class="nf">1</span> <span class="c1">; White noise signal</span>
a<span class="n">sig</span> <span class="nb">rand</span> <span class="mf">0.6</span>
<span class="nb">outs</span> a<span class="n">sig</span><span class="p">,</span> a<span class="n">sig</span>
<span class="kd">endin</span>
<span class="kd">instr</span> <span class="nf">2</span> <span class="c1">;filtered noise</span>
a<span class="n">sig</span> <span class="nb">rand</span> <span class="mi">1</span>
a<span class="n">bp</span> <span class="nb">butterbp</span> a<span class="n">sig</span><span class="p">,</span> <span class="mi">2000</span><span class="p">,</span> <span class="mi">100</span> <span class="c1">;passing only 1950 to 2050 Hz</span>
<span class="nb">outs</span> a<span class="n">bp</span><span class="p">,</span> a<span class="n">bp</span>
<span class="kd">endin</span>
<span class="nt"></CsInstruments></span>
<span class="nt"><CsScore></span>
<span class="nb">i</span> <span class="mi">1</span> <span class="mi">0</span> <span class="mi">2</span>
<span class="nb">i</span> <span class="mi">2</span> <span class="mf">2.5</span> <span class="mi">2</span>
<span class="nb">e</span>
<span class="nt"></CsScore></span>
<span class="nt"></CsoundSynthesizer></span>
</pre>
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<p><br class="example-break" />
</p>
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<div class="refsect1">
<a id="idm281472948624296"></a>
<h2>See Also</h2>
<p>
<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>,
<a class="link" href="butterlp.html" title="butterlp"><em class="citetitle">butterlp</em></a>
</p>
</div>
<div class="refsect1">
<a id="idm281472948620264"></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>
<tr>
<td>1995</td>
</tr>
</table>
<p>
</p>
<p>Existed in 3.30</p>
<p>Audio rate parameters introduced in version 6.02</p>
<p>October 2013.</p>
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