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Bar (music)

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In musical notation, a bar, also known as a measure, is a fundamental segment of music.

Barlines
Barlines

It is bounded by vertical lines called bar lines. These lines indicate one or more recurring beats within a piece. The length of a bar is determined by the number of note values it contains. This specific length is usually indicated by the time signature. Bars help organize rhythm and create a sense of structure for the performer. They allow musicians to group beats into predictable, manageable units.

Bar lines function through several specific visual types. A regular bar line is a thin vertical line. It extends from the top line to the bottom line of the staff. In an orchestral score, it may also extend between different staves. A double bar line consists of two single bar lines drawn close together. This type of line separates two different sections within a musical piece. If a double bar is followed by a thicker line, it indicates the end of a movement or a piece.

Barlines
Barlines

Musicians also use special symbols to manage repetitions and complex notation. A repeat sign looks like a double bar line but includes two dots. These dots are placed one above the other. This symbol tells the musician to repeat the preceding section of music. A begin-repeat sign marks the exact start of the repeated passage. If this sign is missing, the repetition starts from the beginning of the piece. Some editors use a mensurstrich for early music. This is a bar line that stretches only between staves rather than through each individual staff.

Barlines
Barlines

Historical developments show how the use of bars has evolved over centuries. In the 15th and 16th centuries, bar lines appeared in keyboard and vihuela music. During this era, they did not reflect a regular meter. They were used only as section divisions or to mark every single beat. Bar lines were introduced to ensemble music in the late 16th century. However, their use remained irregular for a long time. It was not until the mid-17th century that bar lines adopted the modern style. At this point, every measure became the same length and was associated with time signatures.

There are specific rules for how musicians count and name these segments. The first metrically complete bar in a piece is called "bar 1" or "m. 1." If a piece begins with an anacrusis, which is an incomplete bar, the following bar is designated as bar 1. Bars found within first or second endings are also numbered consecutively. If many consecutive bars contain only rests, they are replaced by a single multirest.

15 bars multirest
15 bars multirest

This symbol includes a number above it to show how many bars it replaces. This keeps the musical score clean and efficient to read.

Within each bar, there is a sense of rhythmic weight. The first note in a bar is known as the downbeat. This note is usually stressed more than the other notes in that bar. Composer Igor Stravinsky noted that bar lines indicate various groupings. These groupings happen rhythmically between beats, between bars, and between musical phrases. This creates a hierarchy of rhythm that helps musicians understand the pulse. Even in complex meters, the bar line provides a vital anchor for the performer.

Music also contains much larger patterns known as hypermeasures.

Hypermeter
Hypermeter

A hypermeasure is a large-scale metric unit or a measure-group. In this system, each regular measure acts as a single beat, or hyperbeat, of a larger meter. This relationship is similar to how a beat relates to a single measure. These hypermeasures must be larger than a single notated bar. They must also consist of a pattern of strong and weak beats. When adjacent hypermeasures are the same length, they create a sense of hypermeter. The term was coined by Edward T. Cone in his 1968 book, Musical Form and Musical Performance. This concept is very similar to the informal idea of a musical phrase.

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File:Barlines.svg
Barlines.svg
File:15 bars multirest.png
15 bars multirest.png
File:Hypermeter.png
Hypermeter.png
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