manual/include/tempo-and-meter.html

<p>
  Tempo and time signature belong together. Without both, there is no way to
  know where a beat lies in time.
</p>

<p>
  Tempo provides a musical pulse, which is divided into beats and bars by a
  time signature. When tempo is changed or an audio-locked time signature is
  moved, all objects on the timeline that are glued to bars and beats
  (locations, regions) will move in sympathy.
</p>

<p class="note">
  When performing time signature or tempo operations, it is advisable to use the
  BBT ruler (available by right-clicking an existing marker or ruler name), and
  ensure that the constraint modifier is set (<kbd class="mod3n"></kbd> by
  default, may be changed in <kbd class="menu">Preferences &gt; Editor &gt;
  Modifiers</kbd>) so that no other modifiers share its key combination. The
  constraint modifier is the "Constrain drags using: " setting under the
  "When Beginning a Drag" heading. One viable setting is
  <kbd class="mod1n"></kbd><kbd class="mod3n"></kbd>.
</p>

<h3>Tempo</h3>

<p>
  Tempo can be adjusted in several ways:
</p>

<ul>
  <li>By double clicking on a tempo marker. This opens the tempo dialog which
  allows entering the tempo directly into an entry box.</li>
  <li>By using the constraint modifier (<kbd class="mod3n"></kbd> by default, 
  may be changed in <kbd class="menu">Preferences &gt; Editor &gt; Modifiers</kbd>)
  to drag the beat/bars in the BBT ruler or the tempo/time signature lines.
  This is the preferred way to match the tempo to previously recorded
  material.</li>

  <p class ="note">
    When dragging the BBT ruler, musical snap has no effect, however be warned
    that non-musical snap is in effect if enabled. Snapping to a minute while
    dragging a beat may result in some very slow tempos. Snapping a beat to a
    video frame however is an incredibly useful way to ensure a soundtrack is
    punchy and synchronized to the sample.
  </p>

  <li>by holding down the constraint modifier while dragging a tempo vertically.
  This is used for more complex tempo solving, as it allows changing of the
  position and tempo of a tempo marker in the same drag; it is, however, a
  useful way to adjust the first tempo for a quick result.</li>
</ul>

<p>
  A tempo may be locked to audio or musical time. This can be changed by <kbd
  class="mouse">right</kbd>-clicking on a tempo. If a tempo is locked to music,
  an entry will be available to lock it to audio. Similarly an audio-locked
  tempo may be locked to music by <kbd class="mouse">right</kbd>-clicking it
  and selecting the "Lock to Music" entry.
</p>

<p>
  Audio locked tempo marks stay in their frame position as their neighbor's
  positions are altered. Their pulse (musical) position will change as their
  neighbors move. Music locked tempo marks move their frame position as their
  neighbors are moved, but keep their pulse position (they will move as the
  music is moved).
</p>

<p>
  A tempo may be constant or ramped:
</p>

<ul>
  <li>A constant tempo will keep the session tempo constant until the next tempo
  section, at which time it will jump instantly to the next tempo. These are
  mostly useful abrupt changes, and is the way in which traditional DAWs deal
  with tempo changes (abrupt jumps in tempo).</li>
  <li>A ramped tempo increases its tempo over time so that when the next tempo
  section has arrived, the session tempo is the same as the second one. This is
  useful for matching the session tempo to music which has been recorded
  without a metronome. Ramps may also be used as a compositional tool, but more
  on this later. Note that a ramp requires two points&mdash;a start and an end
  tempo. The first tempo in a new session is ramped, but appears to be constant
  as it has no tempo to ramp to. It is only when a new tempo is added and one
  of them is adjusted that a ramp will be heard. The same applies to the last
  tempo in the session&mdash;it will always appear to be constant until a new
  last tempo is added and changed.</li>
</ul>

<figure>
    <img src="/images/constant-tempo.png" alt="A constant tempo displaying the
    tempo at the playhead in the audio clock">
    <figcaption>
      A series of constant tempo markers. The tempo at the playhead position is
      the same as the previous tempo.
    </figcaption>
</figure>

<figure>
    <img src="/images/ramped-tempo.png" alt="A ramped tempo displaying the tempo
    at the playhead in the audio clock">
    <figcaption>
        A ramped tempo marker. The tempo at the playhead position is approaching
        the second tempo. Because the playhead is equidistant (in beats) between
        the two markers, the tempo at the playhead is the average of the two.
    </figcaption>
</figure>

<p>
  To add a new tempo, <kbd class="mod1 mouse">right</kbd>-click on the tempo line at
  the desired position. The new tempo will be the same as the tempo at the
  position of the mouse click (it will not change the shape of the ramp).
</p>

<p>
  To copy a tempo, use <kbd class="mod1 mouse">right</kbd> button to drag the tempo to be
  copied.
</p>

<h3>Time signature</h3>

<p>
  Time signature positions beats using the musical pulse of a tempo, and groups
  them into bars using its number of divisions per bar.
</p>

<p>
  The first time signature in a new session may be moved freely. It has an
  associated tempo which cannot be dragged by itself (although all others can).
  It can be moved freely and is locked to audio.
</p>

<p>
  New time signatures are locked to music. They may only occur on a bar line if
  music locked.
</p>

<p>
  An audio locked time signature provides a way to cope with musical passages
  which have no time signature (rubato, pause), or to allow a film composer to
  insert a break in music which cannot be counted in beats.
</p>

<p>
  If a time signature is audio-locked, its bar number is fixed from the point at
  which it left the main score. That bar number cannot be changed, nor can tempo
  motion allow the previous bar to overlap. If another bar is needed, lock the
  time signature to music again (<kbd class="mouse">right</kbd> &gt;
  <kbd class="menu">Lock to Music</kbd>), drag the time signature to the desired
  bar and re-lock to audio. The new bar can be freely dragged again.
</p>

<ul>
  <li>To change a time signature, double-click it. A dialog will appear.</li>
  <li>To copy a time signature, hold down <kbd class="mod1n"></kbd> and drag it.</li>
</ul>