manual/include/corresponding-regions-selection.html

<p>
  <a href="@@the-track-and-bus-group-list">Track Groups</a> have
  a property titled <kbd class="option">Select</kbd> which, if enabled, cause
  Ardour to propagate a region selection in one track of a group to the
  <dfn>corresponding regions</dfn> of the other tracks in that group.
 </p>
<p>
  This can be particularly useful when an instrument has been recorded using
  multiple microphones (e.g. a drum kit): by enabling the <kbd class="option">Select</kbd>
  property for the group, selecting a region in one of the tracks, Ardour will select
  the corresponding region in every other track of the group, which in turn means
  that a subsequent edit operation will affect all the tracks together.
</p>

<h2>How Ardour Decides Which Regions are "Corresponding"</h2>
<p>
  Regions in different tracks are considered to be corresponding for the purposes
  of sharing <dfn>selection</dfn> if they satisfy <em>all</em> the following criteria:
</p>
<ol>
  <li>each region starts at the <dfn>same offset</dfn> within its source file,</li>
  <li>each region is located at the <dfn>same position</dfn> on the timeline, and</li>
  <li>each region has the <dfn>same length</dfn>.</li>
</ol>

<h2>Overlap Correspondence</h2>
<p>
  Sometimes, the rules outlined above are too strict to get Ardour to consider regions
  as corresponding. Regions may have been trimmed to slightly different lengths,
  or positioned slightly differently, and this will cause Ardour to not select
  regions in other grouped tracks.
</p>
<p>
  In this case, changing
  <kbd class="menu">Edit &gt; Preferences &gt; Editor &gt; Regions in
  active edit groups are edited together:</kbd> to <kbd
  class="menu">whenever they overlap in time</kbd> will allow regions in different
  tracks to be considered equivalent for the purposes of selection if they
  <dfn>overlap</dfn>. This is much more flexible and will cover almost all of the
  cases that the fixed rules above might make cumbersome.
</p>