<!-- Converted to DocBook/SGML by Kevin Conder -->
<refentry id="tbvcf">
  <refmeta>
    <refentrytitle>tbvcf</refentrytitle>
  </refmeta>
 
  <refnamediv>
    <refname>tbvcf</refname>
    <refpurpose>
       Models some of the filter characteristics of a Roland TB303 voltage-controlled filter.
      <indexterm id="IndexTbvcf"><primary>tbvcf</primary></indexterm>
    </refpurpose>
  </refnamediv>
 
  <refsect1>
    <title>Description</title>
    <para>
      This opcode attempts to model some of the filter characteristics of a Roland TB303 voltage-controlled filter. Euler's method is used to approximate the system, rather than traditional filter methods. Cutoff frequency, Q, and distortion are all coupled. Empirical methods were used to try to unentwine,  but frequency is only approximate as a result. Future fixes for some problems with this opcode may break existing orchestras relying on this version of <emphasis>tbvcf</emphasis>.
    </para>
  </refsect1>
 
  <refsect1>
    <title>Syntax</title>
    <synopsis>ar <command>tbvcf</command> asig, xfco, xres, kdist, kasym</synopsis>
  </refsect1>
 
  <refsect1>
    <title>Performance</title>
    <para>
      <emphasis>asig</emphasis> -- input signal. Should be normalized to &plusmn;1.
    </para>

    <para>
      <emphasis>xfco</emphasis> -- filter cutoff frequency. Optimum range is 10,000 to 1500. Values below 1000 may cause problems.
    </para>

    <para>
      <emphasis>xres</emphasis> -- resonance or Q. Typically in the range 0 to 2.
    </para>

    <para>
      <emphasis>kdist</emphasis> -- amount of distortion. Typical value is 2. Changing <emphasis>kdist</emphasis> significantly from 2 may cause odd interaction with <emphasis>xfco</emphasis> and <emphasis>xres</emphasis>.
    </para>

    <para>
      <emphasis>kasym</emphasis> -- asymmetry of resonance. Typically in the range 0 to 1.
    </para>
  </refsect1>
 
  <refsect1>
    <title>Examples</title>
    <para>
      Here is an example of the tbvcf opcode. It uses the files <ulink url="examples/tbvcf.orc"><citetitle>tbvcf.orc</citetitle></ulink> and <ulink url="examples/tbvcf.sco"><citetitle>tbvcf.sco</citetitle></ulink>.

      <example>
        <title>Example of the tbvcf opcode.</title>

        <programlisting>
<inlinemediaobject>
            <imageobject>
              <imagedata fileref="examples/tbvcf.orc" format="linespecific">
            </imageobject>
          </inlinemediaobject>
        </programlisting>

        <programlisting>
<inlinemediaobject>
            <imageobject>
              <imagedata fileref="examples/tbvcf.sco" format="linespecific">
            </imageobject>
          </inlinemediaobject>
        </programlisting>
      </example>
    </para>
  </refsect1>
 
  <refsect1>
    <title>Credits</title>
    <para>
      <simplelist>
        <member>Author: &namehans;</member>
        <member>December, 2000 -- January, 2001</member>
      </simplelist>
    </para>

    <para>New in Csound 4.10</para>
  </refsect1>
</refentry>
