Bar (music)

In musical notation, a bar (or measure) is a segment of music bounded by vertical lines, known as bar lines (or barlines), usually indicating one of more recurring beats. The length of the bar, measured by the number of note values it contains, is normally indicated by the time signature. A double bar line (or double bar) consists of two single bar lines drawn close together, separating two sections within a piece, or a bar line followed by a thicker bar line, indicating the end of a piece or movement. Note that double bar refers not to a type of bar (i.e., measure), but to a type of bar line. Another term for the bar line denoting the end of a piece of music is music end. Typically, a double bar is used when followed by a new key signature, whether or not it marks the beginning of a new section. A repeat sign (or, repeat bar line) looks like the music end, but it has two dots, one above the other, indicating that the section of music that is before is to be repeated. The beginning of the repeated passage can be marked by a begin-repeat sign; if this is absent, the repeat is understood to be from the beginning of the piece or movement. This begin-repeat sign, if appearing at the beginning of a staff, does not act as a bar line because no bar is before it; its only function is to indicate the beginning of the passage to be repeated. A mensurstrich is a bar line which stretches only between staves of a score, not through each staff; this is a specialized notation used by editors of early music to help orient modern musicians when reading music which was originally written without bar lines.Some composers use dashed or dotted bar lines; others (including Hugo Distler) have placed bar lines at different places in the different parts to indicate different stress patterns from part to part. If many consecutive bars contain only rests, they may be replaced by a single bar containing a multirest, as shown at right. The number above shows the number of bars replaced.