livetrax/manual/xml/working_with_crossfades.xml

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<section id="sn-working-with-crossfades">
  <title>Working with Crossfades</title>
  <para>
    Whenever you arrange any two audio regions so that they overlap in any
    way, you create the potential for a
    <link linkend="gt-crossfade">crossfade</link> between them: a smooth
    transition from one region to the other. Crossfades in Ardour are
    generated in realtime, and are not stored on disk. They are objects
    within a playlist just like regions, except that the only way to create
    a crossfade is by overlapping two regions, and the only way to remove a
    crossfade is to move one or both of the regions so that they no longer
    overlap. Note that crossfades are not always audible (they can be muted
    and unmuted at will), and can be edited in a variety of ways. We think
    of a crossfade as consisting of an overlap between two regions, plus two
    gain control curves that control the volume of the incoming and outgoing
    regions during the crossfade.
  </para>

  <section id="crossfade-types">
    <title>Types of crossfades</title>
    <para>
      Ardour comes with two basic kinds of crossfades, termed
      <emphasis>short crossfades</emphasis> and <emphasis>full
      crossfades</emphasis> . A full crossfade is a transition between two
      regions that spans the entire overlap between them. If the overlap is
      2 seconds long, then the crossfade is 2 seconds long. A short
      crossfade is a transition between two regions that lasts a fixed
      amount of time and serves simply to avoid audio glitches at the
      boundary of the two regions. The length of a short crossfade is a
      session-wide parameter than can be set via the <emphasis>option
      editor</emphasis> . The default is 15ms, and the length can vary from
      1 milliseconds to 0.5 seconds. In the current version of Ardour, it is
      not possible to change the length of a short becrossfade after it has
      been created, but it is possible to change most short crossfades to a
      full crossfade and vice versa. Full crossfades can have their length
      altered by changing the extent of the overlap between the two regions.
    </para>

    <para>
      Note that even though the absolute length of the crossfade is fixed,
      crossfades can be <emphasis>edited</emphasis> with complete freedom,
      allowing you change the effective length of a crossfade by altering
      the shapes of the fade in and fade out curves.
    </para>
  </section>

  <section id="crossfade-overlaps">
    <title>Overlaps</title>
    <para>
      There are several different ways to overlap two regions, and they
      result in different kinds of crossfades being placed at the boundaries
      of the two regions:
    </para>

    <section id="external-overlaps">
      <title>External overlaps</title>
      <para>
        An "external" overlap occurs when a region starts within another
        region, but extends beyond the other's end.
      </para>
      <mediaobject>
        <imageobject>
          <imagedata fileref="images/overlaplaterhigher.png"/>
        </imageobject>
      </mediaobject>
      <para>
        Overlaps like this will cause an xfade to be placed at the start of
        the later region. Whether it is a full or short crossfade is
        controlled by the current crossfade type preference. If short
        crossfades have been chosen, the crossfade will last for the current
        short crossfade duration; otherwise the full crossfade will last for
        the entire overlap. The mute status of the crossfade will depend on
        the current state of the "New crossfades are muted" setting.
      </para>

      <para>
        In the example above, the later region is above the earlier one. It
        is also possible to create an overlap where the earlier region is in
        a higher layer:
      </para>
      <mediaobject>
        <imageobject>
          <imagedata fileref="images/overlapearlyhigher.png"/>
        </imageobject>
      </mediaobject>
      <para>
        For an overlap of this type, the current crossfade type preference
        affects the placement of the crossfade. If full crossfades have been
        chosen, the crossfade will be placed at the start of the later
        region and will last for the entire overlap. If short crossfades
        have been chosen, the crossfade will start just before the end of
        the earlier region and will last for the chosen short crossfade
        duration. The mute status of the crossfade will depend on the
        current state of the "New crossfades are muted" setting.
      </para>
    </section>

    <section id="internal-overlaps">
      <title>Internal overlaps</title>
      <para>
        An "internal" overlap occurs when the start and end of one region
        both occur within the duration of another.
      </para>
      <mediaobject>
        <imageobject>
          <imagedata fileref="images/internalhigheroverlap.png"/>
        </imageobject>
      </mediaobject>
      <para>
        Overlaps of this type will cause two short crossfades to be place at
        the start of the later region and close to its end. Both crossfades
        will last for the current short crossfade duration, and are created
        in an un-muted state. These crossfades <emphasis>cannot</emphasis>
        be converted to full crossfades. It is important to realize that the
        purpose of these two crossfades is a little different than those
        created for the single-ended overlap cases above. They are created
        solely to avoid audio glitches at the transitions between the two
        regions, and are not intended to facilitate interesting crossfades
        between the upper and lower region.
      </para>

      <para>
        Notice that in the example above, the shorter region is above the
        longer one. It is also possible to create the following type of
        overlap, where the shorter region is below the longer one:
      </para>
      <mediaobject>
        <imageobject>
          <imagedata fileref="images/internalloweroverlap.png"/>
        </imageobject>
      </mediaobject>
      <para>
        Overlaps of this type will not cause any crossfades to be created.
        The uppermost region will be audible throughout its duration; the
        lowermost region will not be audible at all.
      </para>
    </section>
  </section>

  <section id="creating-crossfades">
    <title>Creating Crossfades</title>
    <para>
      To create a crossfade between two regions, move them so that they
      overlap. A crossfade is automatically created within the overlap
      (possibly two, dependening on the type of overlap, as explained
      above). Whether the crossfade is muted or not depends on two things:
    </para>

    <itemizedlist>
      <listitem>
        <para>
          if the current crossfade type is set to "Short", the new crossfade
          will be created in an un-muted state
        </para>
      </listitem>

      <listitem>
        <para>
          if the current crossfade type is set to "Full", the mute status of
          the new crossfade is controlled from the <emphasis>option
          editor</emphasis> on the "Layers&amp;Fades" control panel. If "New
          crossfades are unmuted", the new crossfade will be unmuted.
        </para>
      </listitem>
    </itemizedlist>

    <para>
      A muted crossfade is not directly visible in the editor window, but
      can be accessed by context clicking within the overlap that it relates
      to. An unmuted crossfade has a yellow background that covers the
      entire overlap (to make its presence obvious at all times), and a pair
      of visible curves that show the gain control curves for the fade.
      These curves may not be visible at a particular zoom level, especially
      for short crossfades.
    </para>
  </section>

  <section id="editing-crossfades">
    <title>Editing Crossfades</title>
    <para>
      To carry out operations on a crossfade, context click anywhere in the
      overlap. For the short crossfades in the "internal" overlap case, you
      will need to zoom in until the crossfade becomes visible, and then
      context click on it. Each crossfade under the mouse pointer (there is
      normally only one) will appear in the context menu, and will lead to a
      submenu offering the following options:
    </para>

    <itemizedlist>
      <listitem>
        <para>
          Mute/Unmute the crossfade
        </para>
      </listitem>

      <listitem>
        <para>
          Edit the crossfade
        </para>
      </listitem>

      <listitem>
        <para>
          change the crossfade from short to full or vice versa
        </para>
      </listitem>
    </itemizedlist>

    <para>
      The last option is not available for the short crossfades in the
      "internal" overlap case.
    </para>
  </section>
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