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<h2>
<span class="refentrytitle">moogvcf</span>
</h2>
<p>moogvcf —
A digital emulation of the Moog diode ladder filter configuration.
</p>
</div>
<div class="refsect1" title="Description">
<a id="id3038870"></a>
<h2>Description</h2>
<p>
A digital emulation of the Moog diode ladder filter configuration.
</p>
</div>
<div class="refsect1" title="Syntax">
<a id="id3038882"></a>
<h2>Syntax</h2>
<pre class="synopsis">ares <span class="command"><strong>moogvcf</strong></span> asig, xfco, xres [,iscale, iskip]</pre>
</div>
<div class="refsect1" title="Initialization">
<a id="id3039618"></a>
<h2>Initialization</h2>
<p>
<span class="emphasis"><em>iscale</em></span> (optional, default=1) -- internal
scaling factor. Use if <span class="emphasis"><em>asig</em></span> is not in the
range +/-1. Input is first divided by <span class="emphasis"><em>iscale</em></span>,
then output is mutliplied <span class="emphasis"><em>iscale</em></span>. Default
value is 1. (New in Csound version 3.50)
</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="id3039655"></a>
<h2>Performance</h2>
<p>
<span class="emphasis"><em>asig</em></span> -- input signal
</p>
<p>
<span class="emphasis"><em>xfco</em></span> -- filter cut-off frequency in Hz. As of version 3.50, may i-,k-, or a-rate.
</p>
<p>
<span class="emphasis"><em>xres</em></span> -- amount of resonance. Self-oscillation occurs when <span class="emphasis"><em>xres</em></span> is approximately one. As of version 3.50, may a-rate, i-rate, or k-rate.
</p>
<p>
<span class="emphasis"><em>moogvcf</em></span> is a digital emulation of the Moog diode ladder filter configuration. This emulation is based loosely on the paper <span class="quote">“<span class="quote">Analyzing the Moog VCF with Considerations for Digital Implementation</span>”</span> by Stilson and Smith (CCRMA). This version was originally coded in Csound by Josep Comajuncosas. Some modifications and conversion to C were done by Hans Mikelson.
</p>
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<th align="left">Warning</th>
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<p>This filter requires that the input signal be normalized to one. This can be easily achieved using <a class="link" href="Zerodbfs.html" title="0dbfs"><em class="citetitle">0dbfs</em></a>, like this:
</p>
<div class="literallayout">
<p>ares <span class="command"><strong>moogvcf</strong></span> asig, kfco, kres, 0dbfs</p>
</div>
<p>You can also use <a class="link" href="moogvcf2.html" title="moogvcf2"><em class="citetitle">moogvcf2</em></a> which defaults scaling to <a class="link" href="Zerodbfs.html" title="0dbfs"><em class="citetitle">0dbfs</em></a>. </p>
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<div class="refsect1" title="Examples">
<a id="id3039757"></a>
<h2>Examples</h2>
<p>
Here is an example of the moogvcf opcode. It uses the file <a class="ulink" href="examples/moogvcf.csd" target="_top"><em class="citetitle">moogvcf.csd</em></a>.
</p>
<div class="example">
<a id="id3039773"></a>
<p class="title">
<b>Example 379. Example of the moogvcf opcode.</b>
</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 moogvcf.wav -W ;;; for file output any platform</span>
<span class="csdtag"></CsOptions></span>
<span class="csdtag"><CsInstruments></span>
<span class="comment">; Initialize the global variables.</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> 1
<span class="comment">; Instrument #1.</span>
<span class="oblock">instr</span> 1
<span class="comment">; Use a nice sawtooth waveform.</span>
asig <span class="opc">vco</span> 32000, 220, 1
<span class="comment">; Vary the filter-cutoff frequency from .2 to 2 KHz.</span>
kfco <span class="opc">line</span> 200, p3, 2000
<span class="comment">; Set the resonance amount to one.</span>
krez <span class="opc">init</span> 1
<span class="comment">; Scale the amplitude to 32768.</span>
iscale <span class="op">=</span> 32768
a1 <span class="opc">moogvcf</span> asig, kfco, krez, iscale
<span class="opc">out</span> a1
<span class="oblock">endin</span>
<span class="csdtag"></CsInstruments></span>
<span class="csdtag"><CsScore></span>
<span class="comment">; Table #1, a sine wave for the vco opcode.</span>
<span class="stamnt">f</span> 1 0 16384 10 1
<span class="comment">; Play Instrument #1 for three seconds.</span>
<span class="stamnt">i</span> 1 0 3
<span class="stamnt">e</span>
<span class="csdtag"></CsScore></span>
<span class="csdtag"></CsoundSynthesizer></span>
</pre>
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</div>
<p><br class="example-break" />
</p>
</div>
<div class="refsect1" title="See Also">
<a id="id3039811"></a>
<h2>See Also</h2>
<p>
<a class="link" href="moogvcf2.html" title="moogvcf2"><em class="citetitle">moogvcf2</em></a>,
<a class="link" href="biquad.html" title="biquad"><em class="citetitle">biquad</em></a>,
<a class="link" href="rezzy.html" title="rezzy"><em class="citetitle">rezzy</em></a>
</p>
</div>
<div class="refsect1" title="Credits">
<a id="id3039844"></a>
<h2>Credits</h2>
<p>
</p>
<table border="0" summary="Simple list" class="simplelist">
<tr>
<td>Author: Hans Mikelson</td>
</tr>
<tr>
<td>October 1998</td>
</tr>
</table>
<p>
</p>
<p>Example written by Kevin Conder.</p>
<p>New in Csound version 3.49</p>
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