Tempo and meter belong together. without both, there is no way to know where a beat lies in time.

Tempo provides a musical pulse, which is divided into beats and bars by a meter. When you change tempo or move an audio-locked meter, all objects on the timeline that are glued to bars and beats (locations, regions) will move in sympathy.

When performing meter or tempo operations, it is advised that you show the BBT ruler (available by right-clicking an existing marker or ruler name), and ensure that the constraint modifier is set (in Preferences->User Interaction) 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 .

Tempo

Tempo can be adjusted in several ways:

• by double clicking on a tempo marker. This opens the tempo dialog which will allow you to enter the tempo directly into an entry box.
• by using the constraint modifier (which is set in Preferences->User Interaction) to drag the beat/bars in the BBT ruler or the tempo/meter lines. This is the preferred way to match the tempo to previously recorded material.

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 verly slow tempos. Snapping a beat to a video frame however is an incredibly useful way to ensure your soundtrack is punchy and synchronised to the sample.

• by holding down the constaint modifier while dragging a tempo vertically. This is used for more complex tempo solving, as it allows you to change 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.

A tempo may be locked to audio or musical time. You may change this by right-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 right clicking it an selecting the "Lock to Music" entry.

Audio locked tempo marks stay in their frame position as their neigbours positions are altered. Their pulse (musical) position will change as their neighbours move. Music locked tempo marks move their frame position as their neighbours are moved, but keep their pulse position (they will move as the music is moved).

A tempo may be remped or constant.

• A constant tempo will keep the sesion 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).
  
• A ramped tempo increases its tempo over time so that when the next tempo section has arrived, the sesion 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 - 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 you add a new tempo and adjust one of them that you will hear a ramp. The same applies to the last tempo in the session - it will always appear to be constant until a new last tempo is added and changed.

A series of constant tempo markers. The tempo at the playhead position is the same as the previous tempo.

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.

To add a new tempo, use the primary modifier and 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).

To copy a tempo, hold down the primary modifier and drag the tempo you wish to copy.

Meter

Meter positions beats using the musical pulse of a tempo, and groups them into bars using its number of divisions per bar.

The first meter 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.

New meters are locked to music. They may only occur on a bar line if music locked.

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

If a meter 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 you need another bar, lock the meter to music again (right click->"Lock to Music"), drag the meter to the desired bar and re-lock to audio. You may now drag your new bar freely again.

Techniques

As a general approach, the best way to control tempo ramps is to use them in pairs.

Lets imagine we want to match the click to a drum performance recorded in 'free time'.
The first thing we need to do is determine where the first beat is. Drag the first meter to that position.

Now the first click will be in time with the first beat. To get all the other beats to align, we listen to the drums and visually locate the position of bar 4. You may wish to place the playhead here.

We then locate bar 4 in the bbt ruler and while holding the constraint modifier, drag it to bar 4 in the drum performance.

We notice that the click now matches the first 4 bars, but after that it wanders off. You will see this reflected in the tempo lines.. they won't quite match the drum hits. We now locate the earliest position where the click doesn't match, and place a new tempo just before this. Two bars later, place another new tempo.

Now while dragging any beat after the second new tempo, watch the drum audio and tempo lines until they align.

Notice what is happeneing here: the tempo previous to your mouse pointer is being changed so that the beat you grabbed aligns with the pointer. Notice that the tempo lines previous to the changed one also move. This is because the previous tempo is ramping to the tempo you are changing. Look further to the left. The tempo lines in the first four bars do not move.

Again, some time later the click will not align. I didn't say this was easy.

Repeat the same technique : add two new tempos and drag the BBT ruler after the newest tempo so that the beats align with the audio again.

In a general sense, adding tempo markers in pairs allows you to 'pin' your previous work while you move further to the right.

Another use case : matching accelerando

Imagine you have some video and have located where your music cue begins. Move the first meter to that frame (you may snap to TC frames, but not music with an audio locked meter).

Find a starting tempo by listening to the click while you drag the meter's tempo vertically using teh constraint modifier.

You have the playhead at point where the dude slams the phone down, and your idea was that 4|1|0 would be good for this, but you want an accelerando to that point.

Add a tempo ar bar 4.

Holding down the constraint modifier, and with snap set to 'TC Frames', grab the BBT ruler just after 4|1|0. Drag the ruler so that 4|1|0 snaps to the 'phone' frame.

Notice what happened : The second tempo was changed.
You had set a musical position for the second tempo marker. It was not aligned with the frame you wanted, so you dragged the BBT ruler, making the second tempo provide enough pulses over the ramp for 4|1|0 to align with the desired frame.

If your ramp doesn't feel correct, you may add more points within it and keep adjusting beat positions in a similar manner.

General

Audio locked meters can be useful when composing, as they allow a continuous piece of music to be worked on in isolated segments, preventing the listening fatigue of a fixed form. Reassembly is left as an excercise for the reader.