In musical notation, a bar or measure is a segment of time defined as a given number of beats of a given duration. The word measure is heard more frequently in the U.S., while bar is used in other English-speaking countries, although musicians generally understand both usages.
A bar line (or barline) is a vertical line which separates bars. A double bar can consist of two barlines together, separating two sections within a piece, or a barline followed by a thicker barline, indicating the end of a piece or movement. A repeat barline looks like the second type of double bar but is preceded by two dots, one above the other, indicating that the preceding section of music is to be repeated. The beginning of the repeated passage can be marked by a begin-repeat barline; if this is absent the repeat is understood to be from the beginning of the piece or movement. This begin-repeat barline, if appearing at the beginning of a staff, does not act as a true barline because no bar precedes it; its only function is to indicate the beginning of the passage to be repeated.
Note that the term double bar refers not to a type of bar, but to a type of barline.
In music with a regular meter, bars represent a periodic pulse in the music. In music employing mixed meters, barlines are instead used to indicate the beginning of rhythmic note groups, but this is subject to wide variation: some composers use dashed barlines, others (including Hugo Distler ) have placed barlines at different places in the different parts to indicate varied groupings from part to part.
Quote: "The bar line is much, much more than a mere accent, and I don't believe that it can be simulated by an accent, at least not in my music." - Igor Stravinsky (DeLone et. al. (Eds.), 1975, chap. 3).
A hypermeasure, large-scale or high-level measure, or measure-group is a metric unit in which, generally, each regular measure is one beat (actually hyperbeat) of a larger meter. Thus a beat is to a measure as a measure/hyperbeat is to a hypermeasure. Hypermeasures must be larger than a notated bar, perceived as a unit, consist of a pattern of strong and weak beats, and along with adjacent hypermeasures, which must be of the same length, create a sense of hypermeter. The term was coined by Edward T. Cone . (Stein 2005, p.18-19, 329)
Barlines came into general use in the 1600s, when music began to be written in score format rather than individual parts. 16th-century usage was primarily restricted to lute and vihuela music, but such barlines typically were not used to indicate a regular meter. (Source: Harvard Dictionary of Music)
- DeLone et. al. (Eds.) (1975). Aspects of Twentieth-Century Music. Englewood Cliffs, New Jersey: Prentice-Hall. ISBN 0130493465.
- Stein, Deborah (2005). Engaging Music: Essays in Music Analysis, Glossary. New York: Oxford University Press. ISBN 0195170105.