Introducing the Bar
In order to represent pitch and tone, music notes need a staff. If you’ll remember from our other lessons, the music staff is a system of five horizontal lines and it provides a foundation for all the beautiful music that we hear. Notes sit on, above, between, and below these lines. But there’s another kind of line that you’ll find in sheet music, and it’s the bar line. This *vertical* line also sits on the staff but it doesn’t indicate pitch or tone. It instead, indicates measures or groups of notes. Measures and music bar lines make sheet music easier to write and read.
To understand the role of the bar line, you can compare it to any type of punctuation that ends a sentence. Imagine for a moment, a paragraph of four or five sentences that doesn’t use any periods, question marks, or exclamation points. As you can see, this paragraph would look more like a gigantic run-on sentence than it would look like a group of complete statements. Punctuation lets us know when its specific parts start and finish. This is similar to what music bars do. Music bars let us know when specific parts of a song start and finish.
Like with our paragraph analogy above, music without bar lines would look as though it played continuously without any indications of rhythm or rest. It would also be difficult to reference because quite often, a conductor, tutor, or music book will ask us to play from “measure five” or “measure eight.” That doesn’t mean that “bar-less” music doesn’t exist or isn’t purposeful. Creative types like to reference such music as unmeasured, where music moves freely without a steady beat.
What’s in a Measure?
The measure usually divides notes into three to four beats each, depending on a song’s signature. If the signature of a song indicates 3/4 time for example, each of its measures will contain three beats. Measures of a song played in 4/4 time then contain four beats each. All of this is of course, applicable to the single bar line. The double bar line and thin double bar line indicate other things.
There’s More Than One Bar
Take the double bar line for instance. Two lines make up the double bar line. One line is thin and it sits in front of a second, thick line. This double bar line sits at the very end of a song’s movement and/or completion. The thin double bar line one the other hand, is made of two thin lines only, and it’s used to indicate sections. Like measures, sections are frequently referenced in practice mode. But when a number sits atop a double bar line, it means its section has changed key or meter.
Another kind of bar line is the repeat bar. Music between a double bar that sits in _front_ of two dots — and a double bar that sits _behind_ two dots (the repeat bar) — is played twice. In complicated pieces, you may find repeat bars *and* repeat endings with accompanying numbers. These numbers tell musicians that there’s more than one ending in a song, and that each successive play ends with a corresponding ending.