Why are measures (aka "bars") important?

Question

Just as an example, let's say we have 60 BPM. So every second there's a beat. Imagine nodding your head every second to this rhythm.

Now isn't that enough information to make a song? If I have a metronome at 60BPM then I can rap over it, or play a melody/harmony over it, without thinking about bars at all.

So why do we take an extra step to group 4 of these beats to make a bar, and then think in terms of bars. Also, say if I change it from (1 bar = 4 beats) to (1 bar = 3 beats), how does that change the song? Because the BPM didn't change.. in the above example, I was just rapping to the metronome.

Edit: When I asked this question it was mainly me trying to produce beats on a DAW and bars/beats/tempo are all over the place and I didn't understand why it was defaulted to four beats in a bar. But it's interesting to read all the different perspectives so answer any way you want.

Answer 1

First, I think that it would be difficult to read a piece of music with no bar lines. The bar lines help to break longer streams of notes into regularized and easily digestible chunks.

But it is also not true that a stream of 16 quarter notes should represent the same thing as four bars of four quarter notes. For example, typically in 4/4 time the One and the Three get accented, but not the Two and the Four; but of the One and the Three, the One gets a slightly stronger accent. On the other hand, in 2/4 time the One gets accented, but not the Two. All Ones receive the same accent, and all the strong beats receive the same accent. Here the feel is different from 4/4 time. A similar thing happens with 3/4 time compared with 6/8 time. In 3/4 time the One gets the accent, and in 6/8 time the One and the Four get the accents, with the One receiving slightly more emphasis. This means that 3/4 time and 6/8 time have different rhythmic feels.

So bar lines convey some information about rhythmic feel as well as helping to organize notes into easily digestible chunks. Maybe you could preserve time signatures and rhythmic feel without bar lines, but it would be very difficult to read rhythms this way.

Additionally, music tends to have a regular underlying pulse. Musical phrases are played against this pulse. Sometimes the same phrase is placed differently in different passages, or even within the same passage, of the same piece of music. The result is that the same phrase can sound different when played in different locations with respect to the pulse. Players are usually very sensitive to this when performing; jazz players often talk about "playing across bar lines" or will play the same phrase starting on different beats or subdivisions. All of this is really about sound and feel. Bar lines provide a way to represent the regular pulse of the music so that the ways in which phrases fit around it can be more easily seen in written music. In the end, bar lines are really a notational device.

Answer 2

Please count 1-2-3-4,1-2-3-4, then at the same tempo (speed/ bpm) count 1-2-3-1-2-3.

If you can't feel or tell the difference, then, you're right, there's no need for bars. If you can, then how will someone else know which is which?

Answer 3

One bar tends to be the smallest time after which there is some repetition in multiple voices. This is quite a bit of an oversimplification, but it is often observable, in approximate form, in many very different genres.

Examples:

• Baroque

  X:1
  C:Johann Sebastian Bach
  T:Orchestral Suite #3, 3: Gavotte
  L:1/8
  M:C|
  K:D
  %%score T1 T2 A B
  V:T1           clef=treble
  V:T2           clef=treble
  V:A            clef=alto
  V:B            clef=bass
  % 1
  [V:T1] A2 af | g4     A2 ge | f4    A2 ec | d2
  [V:T2] F2 fd | e4     E2 ec | d4    D2 E2 | A,2
  [V:A]  D2 D2 | A4     A2 A2 | A4    A2 C2 | F2
  [V:B]  (D,4   | D,2) C,B,, C,2 A,,2| D,2 D,,E,, F,,2 G,,E,, | F,,2
  

  Here, the melody voices sequence down the motiv with minim on the 1 and quavers on the 4, the middle voices repeat the simple minim-crotchet-crotchet pattern, and the bass puts quavers on the 2.

• Classical/Romantic:

  X:1
  C:Felix Mendelssohn
  T:Symphony #1, 4: Trio
  L:1/4
  M:6/4
  K:Ab
  %%score O T1 T2 B
  V:O            clef=treble
  V:T1           clef=treble
  V:T2           clef=treble
  V:B            clef=bass
  % 1
  [V:O ] [Ec]6            | [FA]6            | [Fd]6            | [Fc]6
  [V:T1] z3       (A c e) | z3       (A d f) | z3       (B d f) | z3                   (A c f)
  [V:T2] (A, C E) z3      | (A, D F) z3      | (B, D F) z3      | (A, C f) z3
  [V:B]  A,, z2    z3      | D, z2     z3      | B,, z2    z3      | F, z2                         z3
  

• Blues / Rock'n'Roll accompaniment pattern

  X:1
  L:1/8
  M:4/4
  K:A
  %%score D G B
  V:D            clef=perc
  V:G            clef=treble-8
  V:B            clef=bass-8
  % 1
  [V:D] (3[Ee]ze (3[Be]ze (3[Ee]ze (3[Be]zE |  (3[Ee]ze (3[Be]ze  (3[Ee]ze (3[Be]zE
  [V:G] [A,EAce]2 [A,EAcf]2 [A,EAcg]2 [A,EAcf]2 | [A,EAce]2 [A,EAcf]2 [A,EAcg]2 [A,EAcf]2
  [V:B] A,,2 C,2  E,2 (3F,zE, |  A,,2 C,2  E,2 (3F,zE,
  

• Reggae groove

  X:1
  L:1/8
  M:4/4
  K:Bm
  %%score D G B
  V:D            clef=perc
  V:G            clef=treble-8
  % 1
  [V:D] ze [Be]2 [Ee]e [Be]e | ze [Be]2 [Ee]e [Be]e
  [V:G] z2 [B,FBdf]2 z2 [B,FBdf]2 | z2 [B,FBdf]2 z2 [B,FBdf]2
  

...

It's also common to only find repetition after two bars, or already after half a bar. However, one bar is pretty much the shortest delay after which a complete repeat of an accompaniment pattern will sound “proper”.

Answer 4

To offer a different perspective from the other excellent answers here, I'll draw an analogy between a piece of music and a piece of prose.

Barlines are separators, just like paragraphs and chapters. You can write a perfectly fine essay in one massive paragraph, without losing any semantics conveyed by the individual words within. The existence of paragraphs and chapters however, make it much easier on the reader. It gives an indicator of when a new idea, a new scene or a new argument begins, thereby demarcating the structure of the essay. Similarly, barlines make the pulse of the piece very clear to the musician at a glance. The placement of barlines depends on the music in question; just as you wouldn't cut this sentence

into two with a paragraph break, you wouldn't change the barline placement from (1 bar = 4 beats) to (1 bar = 3 beats), if your music rhythmically repeats once every 4 beats. Barlines assist musicians by providing a guide to the rhythm of the music.

Barlines also aid in referencing. Just as it is convenient to refer to a passage in the book by its chapter number, musicians often refer to music by the bar number. This comes in useful especially in a group rehearsal setting, in order for everyone to begin rehearsing from the same point midway through the piece.

Answer 5

Well, in a way, you don't need bars. Not for the sort of thing you were describing. If you just set a metronome up and start rapping away, you probably won't have any problems. But if you want to rap with a band, or anyone else, or if you want to write your music down, bars are necessary. There are several reasons for the concept of bars:

• Communicating metrical information. With your 60 BPM example, changing the meter actually does affect a lot about the song. Think about a waltz vs. a march. In a waltz, which is in 3, you count

1 2 3 |1 2 3...

With an assumed metrical accent on the first beat of each measure. A stead pulse from a metronome does not carry this information.

What if you had it in groups of four? Then, in most western circles, you would get:

1 2 3 4 |1 2 3 4...

In these examples the BPM did not change, however the feel of the song would dramatically change.

Once again, this is not communicated by a steady pulse from a metronome. Now, if you were rapping or singing or playing by yourself, you would almost undoubtedly use one of these, or another simple/compound meter, though you may not realize it. This is fine. But if you want to play with a group, especially if they're sight-reading something that you wrote, having the concept of bars coupled with time signatures is necessary.

• Sight reading. You might be wondering why we can't just write out which beats are stronger without measures, and technically, we can. It's just really hard to read. Bars break the information down. It's much easier to feel measures than it is to theoretically know that certain beats are stronger than others. In a way, when playing as a group, nobody's really thinking that hard about measure, measure, measure, but counting becomes a lot easier when the numbers stay smaller.

• Rehearsal. In orchestral settings, rehearsing one long stream of music would be quite challenging. First of all, if you got lost, it would really suck. Second of all, there's a lot of stop and go in rehearsals, and having measures as reference points, which give each beat their own unique feel in relation to the others (more having to do with meters) is profoundly useful. Thirdly, conducting is a lot more helpful when the conductor can show each beat in a measure by waving his hands in a different direction. For our 4 beats example, the conductor might show

DOWN right left up

With measureless music (which, actually, does exist) this isn't an option.

At the end of the day, measures are descriptive of the way we hear music and rhythm. They are also helpful for studying music as a group or even an individual because they allow places of reference.

Answer 6

Bars also make it easier to find and communicate reference points :

"Let's start again on bar 34"

Someone might count "1…2…3…4…" of bar 33 and everybody in the band will know exactly which note they should start with, and when to play it.

Answer 7

You'll actually find that more often than not, bars then occur in multiples of 8. Music is structured by rhythm. Where it gets interesting is when stuff works "against the beat" but just cannot escape it. Usually this works by having a "rhythm section" establishing the framework that melody instruments (or voices) then move comparatively freely in without losing their reference.

It's also common for the rhythm section to change harmonies on dependable positions within the meter.

By the way: most dancers would be pretty unhappy not having larger structures than single beats since it makes getting into a dance's meter and impetus gain and arrest much harder to work with if you don't have anything to depend on.

Answer 8

Music is counted in beats, it is also counted in bars. Count a march - Left right Left right, One two, One two. Now count a waltz - One two three, One two three. That is why we sometimes group the beats in twos, sometimes in threes.

(Other bar lengths are also used, but they lack similarly neat illustrations.)

Answer 9

When the music is a song set to words, the accentuation implied by the bar lines is usually closely related to the rhythmic meter of the lyrics. For example:

We all know that this is stressed as

God save our gracious Queen / Long live our noble Queen

But it would be quite possible to set it to a different tune as

God save our gracious Queen / Long live our noble Queen

and this would need different bar lines to reflect the different stress in the music.

Answer 10

It's understandable that rap might not be as dependent on a division of beats into bars as other types of music. Rap can flow a lot more freely, and the words might or might not be arranged in phrases, verses or stanzas of the same length.

In other types of music the way the emphasis and phrasing are repeated is more important. In some cases there is a relationship between the music and the dancing that was popular at different times. A waltz is a dance step that repeats the same three steps over and over again, and the music that was played for a waltz did the same thing, repeated three beats over and over again. Bars were a way of keeping those three beats organized. Everybody danced the same three steps and the music helped them keep together.

So, while some types of music might not need such a strict structure, others are dependent on it for their identity.