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<refentry id="atone">
  <refmeta>
    <refentrytitle>atone</refentrytitle>
  </refmeta>
 
  <refnamediv>
    <refname>atone</refname>
    <refpurpose>
      A notch filter whose transfer functions are the complements of the tone opcode.
      <indexterm id="IndexAtone"><primary>atone</primary></indexterm>
    </refpurpose>
  </refnamediv>
 
  <refsect1>
    <title>Description</title>
    <para>
      A notch filter whose transfer functions are the complements of the tone opcode.
    </para>
  </refsect1>
 
  <refsect1>
    <title>Syntax</title>
    <synopsis>ar <command>atone</command> asig, khp [, iskip]</synopsis>
  </refsect1>
 
  <refsect1>
    <title>Initialization</title>
    <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>khp</emphasis> --  the response curve's half-power point, in Hertz. Half power is defined as peak power / root 2. 
    </para>

    <para>
      <emphasis>atone</emphasis> is a filter whose transfer functions is the complement of <link linkend="tone"><citetitle>tone</citetitle></link>. <emphasis>atone</emphasis> is thus a form of high-pass filter whose transfer functions represent the <quote>filtered out</quote> aspects of their complements. However, power scaling is not normalized in <emphasis>atone</emphasis> but remains the true complement of the corresponding unit. Thus an audio signal, filtered by parallel matching <emphasis>tone</emphasis> and <emphasis>atone</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 atone opcode. It uses the files <ulink url="examples/atone.orc"><citetitle>atone.orc</citetitle></ulink> and <ulink url="examples/atone.sco"><citetitle>atone.sco</citetitle></ulink>.

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

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

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

  <refsect1>
    <title>See Also</title>
    <para>
      <link linkend="areson"><citetitle>areson</citetitle></link>,
      <link linkend="aresonk"><citetitle>aresonk</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>
