opcodes/noise.xml


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<refentry id="noise">
<indexterm id="IndexNoise"><primary>noise</primary></indexterm>
  <refentryinfo><title>Signal Generators:Random (Noise) Generators</title></refentryinfo>
  <refmeta>
    <refentrytitle>noise</refentrytitle>
  </refmeta>


  <refnamediv>
    <refname>noise</refname>
    <refpurpose>
      A white noise generator with an IIR lowpass filter.
          </refpurpose>
  </refnamediv>
 
  <refsect1>
    <title>Description</title>
    <para>
      A white noise generator with an IIR lowpass filter.
    </para>
  </refsect1>
 
  <refsect1>
    <title>Syntax</title>
    <synopsis>ares <command>noise</command> xamp, kbeta</synopsis>
  </refsect1>
 
<!--  <refsect1>
    <title>Initialization</title>
  </refsect1>-->
 
  <refsect1>
    <title>Performance</title>
    <para>
      <emphasis>xamp</emphasis> -- amplitude of final output
    </para>

    <para>
      <emphasis>kbeta</emphasis> -- beta of the lowpass filter. Should be in the range of -1 to 1.
    </para>

    <para>
      The filter equation is:
      <mediaobject>
        <imageobject>
          <imagedata fileref="images/noise-filter.png" format="PNG"/>
        </imageobject>

        <textobject>
          <phrase>[Filter equation for filter in noise opcode.]</phrase>
        </textobject>

<!--        <caption>
          <para>A diagram showing the Poisson distribution.</para>
        </caption>-->
      </mediaobject>

      where <emphasis>x<subscript>n</subscript></emphasis> is the original white noise and <emphasis>y<subscript>n</subscript></emphasis> is lowpass filtered noise. The higher &beta; is, the lower the filter's cut-off frequency. The cutoff frequency is roughly sr * ((1-kbeta)/2).
    </para>
  </refsect1>

  <refsect1>
    <title>Examples</title>
    <para>
      Here is an example of the noise opcode. It uses the file <ulink url="examples/noise.csd"><citetitle>noise.csd</citetitle></ulink>.

      <example>
        <title>Example of the noise 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/noise.csd.xml" xmlns:xi="http://www.w3.org/2001/XInclude"/>
      </example>
    </para>
    <para>
      Here is an example of the noise opcode controlling the kbeta parameter with a GUI interface. It uses the file <ulink url="examples/noise-2.csd"><citetitle>noise-2.csd</citetitle></ulink>.

      <example>
        <title>Example of the noise opcode controlled with a GUI.</title>

          <xi:include href="examples-xml/noise-2.csd.xml" xmlns:xi="http://www.w3.org/2001/XInclude"/>
      </example>
    </para>
  </refsect1>
 
  <refsect1>
    <title>Credits</title>
    <para>
      <simplelist>
        <member>Author: &namejohn;</member>
        <member>University of Bath, Codemist. Ltd.</member>
        <member>Bath, UK</member>
        <member>December 2000</member>
      </simplelist>
    </para>
    <para>Example written by &namekevin;.</para>

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