How long is a bar?

Philtre

This should simplify things:

digitalkettle

Philtre said:

This should simplify things:

Easy...duration = 2’53

merlin

digitalkettle said:

Philtre said:

This should simplify things:

Easy...duration = 2’53

Or if you turn the volume all the way down, duration = 4'33".

UnclePsychosis

Most explanations I've seen of this always really overcomplicate it. 

In a time signature, the "bottom" number tells you which note value represents the unit of beats (which is easier to remember if you speak American (eighth, fourth, etc) rather than everyone else (quaver, crotchet,etc). The "top" number tells you how many of those note values make up a bar.

So 4/4 time is a time signature which has four fourth notes (crotchets) per bar. 
Similarly, 3/4 time has three fourth notes (crotchets) per bar.
3/8 time would have three eighth notes (quavers) per bar. 
6/8 has six eighth notes (quavers) per bar
12/8 has twelve eighth notes (quavers) per bar. 

Time signatures which have a 2, 3, or 4 on the top are called "simple" time. Simple in this context means each beat can be split into two notes. 

Time signatures which have a 6, 12, or sometimes a 9 on the top are called "compound" time. (these are almost always accompanied by an 8 on the bottom). In compound time, beats are split into three which gives a triplet feel. 

The difference between 3/4 and 6/8 can be felt in the counting. 

In 3/4 you would count two bars as One and Two and Three and One and Two and Three and (imagine emphasis on the bold beats). 3/4 has three beats in a bar, with each beat splits into two parts. 

In 6/8 you would count two bars as One and a Two and a One and a Two and a. Each beat is a triplet, so it feels different to 3/4---6/8 has two beats in a bar, with each beat split into three parts.  

4/4 and 12/8 have the same relationship as 3/4 and 6/8. 

 In answer to the specific question of "how long is a bar"---well its answered by the time signature. In 3/4 time a bar consists of three crotchets. In 6/8 it consists of six quavers. In 4/4 it consists of four crotchets. That's all there is to it. 

WiresDreamDisasters

Length of a bar in seconds is related to the tempo.

At 120bpm, an eighth note is 250milliseconds long. a quarter note is 500milliseconds long.

So one bar of 4/4 would be 500x4 = 2000milliseconds long; or 2 seconds.

One bar of 4/8 would be 250x4 = 1000milliseconds, or 1 second long.

Teetonetal

You could try thinking of it like this.

Tempo is 60 beats per min

Now 1 beat lasts 1 second

count the seconds in groups of 3 = 3/4 time (1,2,3 2,2,3 3,2,3 etc)
count the seconds in groups of 4 = 4/4 time (1,2,3,4 ,2,2,3,4 3,2,3,4 etc)

At the end of min, you have played 60 beats in both cases. But they will feel different. In either case, the group or 3 or 4 will be 1 complete bar.

if you speed up or slow down the tempo, you are simply altering the length of time one beat last for. could be .5 of a second, could be 1.5 seconds, but that will determine the pace of the song.

Simple explanation, but clear (I think)

Funkfingers

Anyone for The Black Page?

Nitefly

I recently had an interesting chat with a drummer (no really), in which we were trying to work out the time signature of the song "America", from West Side Story.

If you recall, it goes "I like to be in America".  The first part (6 syllables, "I Like to be in A") is fairly obviously 6/8, played as two triplets as mentioned above. 

But then the last three syllables "me-ri-ca" feel very different, as it's 3 lots of 2 beats.  

We thought it must still be 6/8, but with a different feel.

Could it in fact be 12/8?  Bloody clever, either way.

viz

It's in 6/8 throughout, but Me Ri Ca are 3 crotchets, so it's basically sort-of as though it's in 3/4 for that bar. 

viz

In fact, like this

https://i.imgur.com/4m24SCb.jpg

Nitefly

Cheers, @viz , that makes sense now.

digitalkettle

‘America’ is a classic example of a hemiola: it’s in 6/8 but you’re hearing two groups of three and three groups of two at the same time (so it’s kind of in 3/4 too). Pretty common in south american classical music (which is probably why it turns up in West Side Story so memorably).

mart

So would it be more correct to say that America is alternating bars of 6/8 and 3/4?

viz

mart said:

So would it be more correct to say that America is alternating bars of 6/8 and 3/4?

sort of, but it’s not really done, it’s better to think of it as a break away from the underlying structure, than 2 alternating structures, and as Mr Digitalkettle says, that 3 beats over an underlying rhythm of 2 is called a hemiola. 

HAL9000

merlin said:

digitalkettle said:

Philtre said:

This should simplify things:

Easy...duration = 2’53

Or if you turn the volume all the way down, duration = 4'33".

Is that the CAGEd method?

PolarityMan

I'd view triplet phrasing in 6/8 as more like a convention. You could have a 2 note phrase followed by 4 note phrase in 6/8 for example. 

If you're changing time sigs a alot it sometimes makes more sense to transcribe something that is genuinely 3/4 into 6/8 so that the pulse (and critically the metronome) is consistent and just because you transcribe the part into a different time signature it doesn't change the way it's performed. 

viz

PolarityMan said:

I'd view triplet phrasing in 6/8 as more like a convention. You could have a 2 note phrase followed by 4 note phrase in 6/8 for example. 

If you're changing time sigs a alot it sometimes makes more sense to transcribe something that is genuinely 3/4 into 6/8 so that the pulse (and critically the metronome) is consistent and just because you transcribe the part into a different time signature it doesn't change the way it's performed. 

Possibly agree that if the time sig, or at least the accentuation, is changing a lot there may be one overarchung sig that is more appropriate than any other alternatives, but in your 2+4 phrased example, I can’t think of an example where 3/4, rather than 6/8, wouldn’t be the most appropriate time sig - can you give an example?

6/8 is meant for 2 main beats, each with 3 triplets. 

PolarityMan

Those were 2 separate examples. So for exame you can have a bar if 6/8 that does not have 2 equally spaced main beats like 4 + 2. Then separately you might have a phrase later in day a 4 bar passage that makes a bar of 3/4 more appropriate to score as 6/8.

viz

PolarityMan said:

Those were 2 separate examples. So for exame you can have a bar if 6/8 that does not have 2 equally spaced main beats like 4 + 2. Then separately you might have a phrase later in day a 4 bar passage that makes a bar of 3/4 more appropriate to score as 6/8.

I don’t really understand; I mean, yes I suppose you could have a phrase that has 2 quavers then 4 quavers in a 6/8 piece, basically like a “pushed” beat. But the general rhythm would still be a 2/4, with triplets, which is what 6/8 means. Like in jazz, triplets on the ride cymbal, and a “pushed” note to come before the 2nd main beat.

And with your 2nd example, yes, if the music moves to a 6/8 rhythm, you can change the time sig to 6/8.

I don’t know where we’re going with this. I have a feeling we’re agreeing on a slightly non issue

TheBigDipper

Music is aural. Music notation is written and explains or documents what we're hearing when it's played (after the fact) or as instructions to the musician (before the fact). But it's not perfect. 

Tempo (when expressed as bpm) is absolute and objective. Old-fashioned Italian tempo instructions like andante and allegretto are not quite as precise. Which is why it's so hard to define how long a bar is, or how much time there should be between crochets.

Time signatures imply the rhythm of the music as well as the tempo. A bar of 3/4 at 60bpm will take the same length of time to hear or play as a bar of 6/8 at 120 bpm (3 seconds), but the rhythm is different, as previously stated. 

I can't see how PolarityMans example of six notes in the bar of equal time value above can be written meaningfully as 6/8, because there's no sense of rhythm in it that implies 6/8. You can write it that way, but wouldn't be meaningful or helpful to a player. It is a convention designed to give  meaning to a player, as well as the way the notes are tied together on the stave. 

I'd write the ONE 2 THREE 4 5 6 example as 3/4, because the main beats drop onto the 1 and the 2 of a crotchet-based rhythm. When they drop on the ONE 2 3 FOUR 5 6 then it's triplets, a quaver-based beat and 6/8 - despite both being one bar of music that takes up the same length of time. 

I didn't do well at music theory classes, BTW....  :-)