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What Is a Bar in Music?
In music theory, a bar (or measure) is a single unit of time containing a specific number of beats played at a particular tempo. Bars are designated by vertical bar lines that run perpendicular to the staff, indicating the beginning and end of the bar. When writing music on a page, composers break their compositions into digestible sections that help players perform the music as intended. When a piece of music is divided into bars, players need only process a little bit of music at a time, allowing them to remain focused on delivering the best possible performance.
1. Single bar line: A single vertical line that indicates the end of one bar and the beginning of another.
2. Double bar line: Two side-by-side vertical lines, indicating the end of one section and the beginning of another.
3. End bar lines: Two vertical lines, the second line thicker than the first. This indicates the end of a musical movement or an entire composition.
4. Start repeat: Double bar lines—the first one thicker than the second—followed by a pair of dots that look like a colon punctuation mark. This indicates the first bar of a repeated section.
5. End repeat: Double bar lines—the second one thicker than the first—preceded by a pair of dots that look like a colon punctuation mark. This indicates the final bar of a repeated section.
How to Read a Bar of Music
A musician reads a bar of music from left to right, playing the notes in sequence as they appear. To read a bar of music, you need to understand the basics of tempo, meter, and note values. The information conveyed within a bar of written music depends on the:
- Time signature: Musical time signatures show the number of beats per measure (the top number in a time signature) and the duration of each beat (the bottom number in the time signature). For instance, 3/4 time indicates that there are three beats per bar and each beat has the duration of a quarter note. The most common time signature in Western music is 4/4 or common time.
- Tempo: Tempo refers to the speed of a section of music. It can be indicated in metronome markings using beats per minute (BPM) or by using descriptive words (traditionally Italian words describe tempo like adagio or andante).
- Note values: Individual notes within a bar last for a specific fraction of the duration of that bar. For instance, quarter notes last for one quarter of a 4/4 bar, while eighth notes last for one eighth of that same 4/4 bar.
- Bar lines: Different types of bar lines indicate different player behavior, from continuing onward to repeating a section to stopping the music altogether.
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