<!-- Converted to DocBook/SGML by Kevin Conder -->
<refentry id="areson">
  <refmeta>
    <refentrytitle>areson</refentrytitle>
  </refmeta>
 
  <refnamediv>
    <refname>areson</refname>
    <refpurpose>
      A notch filter whose transfer functions are the complements of the reson opcode.
      <indexterm id="IndexAreson"><primary>areson</primary></indexterm>
    </refpurpose>
  </refnamediv>
 
  <refsect1>
    <title>Description</title>
    <para>
      A notch filter whose transfer functions are the complements of the reson opcode.
    </para>
  </refsect1>
 
  <refsect1>
    <title>Syntax</title>
    <synopsis>ar <command>areson</command> asig, kcf, kbw [, iscl] [, iskip]</synopsis>
  </refsect1>
 
  <refsect1>
    <title>Initialization</title>
    <para>
      <emphasis>iscl</emphasis> (optional, default=0) -- coded scaling factor for resonators. A value of 1 signifies a peak response factor of 1, i.e. all frequencies other than kcf are attenuated in accordance with the (normalized) response curve. A value of 2 raises the response factor so that its overall RMS value equals 1. (This intended equalization of input and output power assumes all frequencies are physically present; hence it is most applicable to white noise.) A zero value signifies no scaling of the signal, leaving that to some later adjustment (see <link linkend="balance"><citetitle>balance</citetitle></link>). The default value is 0.
    </para>

    <para>
      <emphasis>iskip</emphasis> (optional, default=0) -- initial disposition of internal data space. Since filtering incorporates a feedback loop of previous output, the initial status of the storage space used is significant. A zero value will clear the space; a non-zero value will allow previous information to remain. The default value is 0.
    </para>
  </refsect1>
 
  <refsect1>
    <title>Performance</title>
    <para>
      <emphasis>ar</emphasis> -- the output signal at audio rate.
    </para>

    <para>
      <emphasis>asig</emphasis> -- the input signal at audio rate.
    </para>

    <para>
      <emphasis>kcf</emphasis> -- the center frequency of the filter, or frequency position of the peak response.
    </para>

    <para>
      <emphasis>kbw</emphasis> -- bandwidth of the filter (the Hz difference between the upper and lower half-power points).
    </para>

    <para>
      <emphasis>areson</emphasis> is a filter whose transfer functions is the complement of <link linkend="reson"><citetitle>reson</citetitle></link>. Thus <emphasis>areson</emphasis> is a notch filter whose transfer functions represents the <quote>filtered out</quote> aspects of their complements. However, power scaling is not normalized in <emphasis>areson</emphasis> but remains the true complement of the corresponding unit. Thus an audio signal, filtered by parallel matching <emphasis>reson</emphasis> and <emphasis>areson</emphasis> units, would under addition simply reconstruct the original spectrum. 
    </para>

    <para>
      This property is particularly useful for controlled mixing of different sources (see <link linkend="lpreson"><citetitle>lpreson</citetitle></link>). Complex response curves such as those with multiple peaks can be obtained by using a bank of suitable filters in series. (The resultant response is the product of the component responses.) In such cases, the combined attenuation may result in a serious loss of signal power, but this can be regained by the use of <link linkend="balance"><citetitle>balance</citetitle></link>.
    </para>
  </refsect1>

  <refsect1>
    <title>Examples</title>
    <para>
      Here is an example of the areson opcode. It uses the files <ulink url="examples/areson.orc"><citetitle>areson.orc</citetitle></ulink> and <ulink url="examples/areson.sco"><citetitle>areson.sco</citetitle></ulink>.

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

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

        <programlisting>
<inlinemediaobject>
            <imageobject>
              <imagedata fileref="examples/areson.sco" format="linespecific">
            </imageobject>
          </inlinemediaobject>
        </programlisting>
      </example>
    </para>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para>
      <link linkend="aresonk"><citetitle>aresonk</citetitle></link>, 
      <link linkend="atone"><citetitle>atone</citetitle></link>, 
      <link linkend="atonek"><citetitle>atonek</citetitle></link>, 
      <link linkend="port"><citetitle>port</citetitle></link>, 
      <link linkend="portk"><citetitle>portk</citetitle></link>, 
      <link linkend="reson"><citetitle>reson</citetitle></link>, 
      <link linkend="resonk"><citetitle>resonk</citetitle></link>, 
      <link linkend="tone"><citetitle>tone</citetitle></link>, 
      <link linkend="tonek"><citetitle>tonek</citetitle></link>
    </para>
  </refsect1>
</refentry>
