Add some sparse documentation for tempo and meter.

_manual/25_tempo-meter.html

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+---
+layout: default
+title: Working with Tempo and Meter
+---
+
+{% children %}

_manual/25_tempo-meter/01_tempo-and-meter.html

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+---
+layout: default
+title: Working with Tempo and Meter
+menu_title: Tempo and Meter
+---
+
+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.
+
+TEMPOS
+
+In PROGRAM_NAME, tempos 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 best used for 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.
+
+Tempos 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 tempos stay in their frame position as their neigbours positions are altered. Their pulse (musical) position will change as their neighbours move.
+Music locked tempos move their frame position as their neighbours are moved, but keep their pulse position (they will move as the music is moved).
+
+Tempos may also 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 click tracks or electronic clocks.
+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.
+
+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.
+
+To change a meter, double click it. A dialog will appear.
+
+To copy a meter, hold down control and drag it.
+
+
+Techniques
+
+As a general approach, the best way to control tempo ramps is to use them in pairs (disregarding the first one).
+
+Lets imagine we want to match PROGRAM_NAMEs 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 alignaed 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 note:
+
+Audio locked meters can be very 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.