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<refentry id="moogvcf">
<indexterm id="IndexMoogvcf"><primary>moogvcf</primary></indexterm>
<refentryinfo><title>Signal Modifiers:Standard Filters:Resonant</title></refentryinfo>
<refmeta>
<refentrytitle>moogvcf</refentrytitle>
</refmeta>
<refnamediv>
<refname>moogvcf</refname>
<refpurpose>
A digital emulation of the Moog diode ladder filter configuration.
</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<para>
A digital emulation of the Moog diode ladder filter configuration.
</para>
</refsect1>
<refsect1>
<title>Syntax</title>
<synopsis>ares <command>moogvcf</command> asig, xfco, xres [,iscale, iskip]</synopsis>
</refsect1>
<refsect1>
<title>Initialization</title>
<para>
<emphasis>iscale</emphasis> (optional, default=1) -- internal
scaling factor. Use if <emphasis>asig</emphasis> is not in the
range +/-1. Input is first divided by <emphasis>iscale</emphasis>,
then output is mutliplied <emphasis>iscale</emphasis>. Default
value is 1. (New in Csound version 3.50)
</para>
<para>
<emphasis>iskip</emphasis> (optional, default=0) -- if non zero
skip the initialisation of the filter. (New in Csound version
4.23f13 and 5.0)
</para>
</refsect1>
<refsect1>
<title>Performance</title>
<para>
<emphasis>asig</emphasis> -- input signal
</para>
<para>
<emphasis>xfco</emphasis> -- filter cut-off frequency in Hz. As of version 3.50, may i-,k-, or a-rate.
</para>
<para>
<emphasis>xres</emphasis> -- amount of resonance. Self-oscillation occurs when <emphasis>xres</emphasis> is approximately one. As of version 3.50, may a-rate, i-rate, or k-rate.
</para>
<para>
<emphasis>moogvcf</emphasis> is a digital emulation of the Moog diode ladder filter configuration. This emulation is based loosely on the paper <quote>Analyzing the Moog VCF with Considerations for Digital Implementation</quote> by Stilson and Smith (CCRMA). This version was originally coded in Csound by Josep Comajuncosas. Some modifications and conversion to C were done by &namehans;.
</para>
<warning>
<para>Before version 6.02 this filter required that the input signal be normalized to one. This can be easily achieved using <link linkend="Zerodbfs"><citetitle>0dbfs</citetitle></link>, like this:
<literallayout>ares <command>moogvcf</command> asig, kfco, kres, 0dbfs</literallayout></para>
<para>You can also use <link linkend="moogvcf2"><citetitle>moogvcf2</citetitle></link> which defaults scaling to <link linkend="Zerodbfs"><citetitle>0dbfs</citetitle></link>. </para>
</warning>
</refsect1>
<refsect1>
<title>Examples</title>
<para>
Here is an example of the moogvcf opcode. It uses the file <ulink url="examples/moogvcf.csd"><citetitle>moogvcf.csd</citetitle></ulink>.
<example>
<title>Example of the moogvcf opcode.</title>
<para>See the sections <link linkend="UsingRealTime"><citetitle>Real-time Audio</citetitle></link> and <link linkend="CommandFlags"><citetitle>Command Line Flags</citetitle></link> for more information on using command line flags.</para>
<xi:include href="examples-xml/moogvcf.csd.xml" xmlns:xi="http://www.w3.org/2001/XInclude"/>
</example>
</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<link linkend="moogvcf2"><citetitle>moogvcf2</citetitle></link>,
<link linkend="biquad"><citetitle>biquad</citetitle></link>,
<link linkend="rezzy"><citetitle>rezzy</citetitle></link>
</para>
</refsect1>
<refsect1>
<title>Credits</title>
<para>
<simplelist>
<member>Author: &namehans;</member>
<member>October 1998</member>
</simplelist>
</para>
<para>New in Csound version 3.49</para>
</refsect1>
</refentry>
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