For a theatrical musician this technique (or bundle of techniques) is the bread and butter of live theatre. These are the buffers that bridge the gap between the prewritten and preplanned score and technology and the unpredictable excitement of the performers and the audience. There are two types of buffer, the Vamp and the Safety Bar/Passage, and while they often look like repeats they are actually very different beasts.
Perhaps we should start with some definitions:
A vamp is a section of music that is repeated several times while dialogue or onstage action occurs. It is usually directed by the conductor’s cue, and as such can cope with the unpredictability of long stretches of dialogue or indeterminable theatrical machinations.
Similar to a vamp, a safety is usually a shorter optional passage designed to accommodate for unplanned hiccups in the performance. Usually added in the score as optional repeats, safeties can occasionally be improvised. As Mark Lubbock recounted in 1957 “the wise conductor arranges a safeguard in the form of a repeat near the end of the number, which can be made if necessary. Then there is the question of music to bring characters on to the stage and actors who miss their entrances and do not appear till the music is nearly finished. One conductor’s solution to this problem was to lean over to his cellos with the instruction, ‘Tremble, boys, ad lib.’, and the gap was filled.”
This is the notation that appears in scores across the spectrum of classical and popular music, and means that the performers play the bracketed section an additional time. It appears mostly as a shorthand used to indicate musical form (multiple verses, repeated exposition in sonata form, etc.) without burdening the performer with unnecessary page turns.
While repeats are found in theatrical music, the most useful tools for a theatrical toolbox are the vamp and the safety.
Vamps can be as short as one beat or as long as a full phrase, but in essence they are a section of music that is looped by the performers while they wait for a cue. This cue can be a line of dialogue, an action, a piece of stagecraft (like a set or prop being flown into place) or the end of an audience reaction. This means that someone (usually a conducter or band leader) is watching and listening to the world around them to decide on the cue for the group, particularly for cues that are a bit nebulous, like the end of audience applause or a scene change. Once the cue has been given the music continues seamlessly into the next section. This is often found in musical theatre as an introduction, with the cue marked as voice last time. This means that the musicians play the music until they hear the vocalist enter, at which point they will continue accompanying the melody.
A safety bar is very similar to a vamp, but is usually only one or two bars long (not a complete phrase) and is hopefully optional. It can be found at the end of a section and exists to cope with emergencies that can arise. For example if a actor needs to enter and sing, or a screen visualisation to get going, a safety can be written in the score. Hopefully the actor will get there on time, and the screen will start on cue, but if they don’t the overall sound will not be compromised. These are slightly tricky to play, as they need good reactions, but they are very useful for safety purposes.
These effects are notated with normal repeat marks at either end of the section to be repeated. This is fine, as long as it is clear how exactly the section should be played. Too often, however, a section of a score will be bracketed with repeat marks, with no indication as to whether the section should be repeated once, vamped until some unknown cue, or simply a section to be repeated only in emergencies. I’ve been guilty of this myself, and it becomes the hardest part of the work to rehearse with the musicians.