# I don't fully understand key signatures. (Beginner)



## trumpetcannon

Let me preface this with I do know how key signatures work. The top number is the number of beats per measure, and the bottom number is the note that has the beat. But I don't understand how someone can tell when the key signature changes in a piece of music by ear. For example, a melody going from 5/4 to 6/4 back to 5/4 back to 6/4, like Promanade from Pictures at an Exhibition by Mussorgsky. In my view, it all still sounds the same, the bar lines are just arranged differently. How can you tell when the key signature changes when transcribing by ear? Also, just as a side note, when composing, why should you change key signatures and how is that useful?

Thank you!


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## Larkenfield

Actually, what you're asking about is _time_ signatures, not key signatures. A key signature is, as you probably already know, whether something is written, for example, in the key of A-minor or B-flat major. Time signatures indicate how many beats will take place within each bar and the value of note that is considered a beat... and it's not always possible to tell by ear when it changes within a piece of music. For instance, the time signatures change a great deal in Stravinsky's Rite of Spring. But it's not always possible to tell by ear when the time signature changes; you have to see the actual published score.

Why change the time signature and divide it up differently? It might sound the same outwardly as a regular time signature, a regular beat, but the different time signatures will emphasize different beats and different accents of beats within what sounds like a regular time signature. It's a different way of thinking and feeling what may sound like a regular beat, but it's doubtful that anyone can tell the changes in time signatures only by ear. Seeing is believing.


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## Guest

First of all, you're talking about time signature not key signature. Time signatures give you the beat. Every bar must have that many beats--no more, no less. If the time signature changes, the bar it changes in is going to have the new time signature starting in that bar. So two bars of 5/4 followed by two bars of 6/4 is going to count:

1-2-3-4-5 / 1-2-3-4-5 / 1-2-3-4-5-6 / 1-2-3-4-5-6

To feel it, snap your fingers in a steady pulse on 2 and 4 on the first bar--every other beat. Count the beats out loud. Notice on the second bar, your fingers are now snapping on 1, 3 and 5 even though you didn't alter the steady beat of your finger snaps. On the 3rd bar, your fingers snap at 2, 4 and 6 and does the same for the 4th bar. That's because you have an even number of beats so your finger snaps fall on the same beats over and over again at bars 3 and 4. Bars 1 and 2 sound and feel very different from bars 3 and 4. That's very important if you're going to play that piece correctly.

There should be no jerky stopping and starting but one bar flowing smoothly to the next at a steady pace and that's what fools you into thinking there's no difference. There's a big difference. If we were playing something with 2 bars of 5/4 followed by 2 bars of 6/4 and I tell you to give me a "C" on 1,3 and 5 on the first two bars and on 2, 4, 6 on the last two bars, how will you do that if you don't know the time signatures? Try it.

To transcribe by ear takes practice. You just _feel_ that time signature out. But on complex pieces, it's always best to have the score or chart with you. Play different pieces whose time signatures you know and start counting it off. Try this with several time signatures. Then try it with some pieces you don't know and look at the sheet music and see if you got it right--you can find a lot of the sheet music online. Once you get used it, you pick it out pretty easy even when it suddenly changes on you. You'll feel it change.


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## EdwardBast

Welcome trumpet cannon.

What you are asking about is time signatures, not key signatures. The purpose of time signatures is to make the metric organization of a piece of music as clear as possible to the performers, and to allow for the division of the score into easily readable units. Each time signature has a long history and standard expectations about how accents are normally to be distributed. In 4/4, for example, one expects 1 to be the strongest beat, 3 to be strong, and 2 and 4 to be weaker. If one hears music consistently exhibiting this pattern of accents, one would likely transcribe it in 4/4. In 3/4 one will most commonly hear patterns of three beats with beat 1 being the strongest and often a secondary stress on 3. Of course, these regular and expected patterns are often broken, disguised or ignored.

In the case of "Promenade," the first part is clearly in repeated phrases of eleven beats. There is no even way to subdivide this, hence the pattern of 5/4 alternating with 6/4. The way Mussorgsky did it is rational and doesn't cause slurs to cross bar lines. If one were transcribing this piece by ear, it is quite possible one might come up with something different. 

When composing it is wise to make the music as easy as possible for performers to read and comprehend. One changes time signature when accomplishing this goal makes it necessary or useful to do so. If one starts out with four beat units but then composes a secondary theme that subdivides into threes, then it will make sense to start in 4/4 and change to 3/4. 

A good exercise would be to listen to different works and try to grasp the subdivisions by ear before consulting the score. One should also learn the standard time signatures for Baroque and Classical dance based movements like minuets, gigues, sarabandes, and so on.


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## millionrainbows

There are rhythms which are difficult for our notation system to intuitively, or simply represent, namely, the blues and jazz rhythms which divide the beat into three parts, instead of two.

That's because our note values are all divisions of two: whole, half, quarter, eighth, sixteenth, thirty-second, and so forth. To get a value of 3, one must put a dot after the note value, as in a "dotted eighth" which represents 3 eighth notes.

However, this "3" value cannot be put into a time signature: the bottom number of a time signature will always be an even number: 2/4, 3/4, 4/4, 5/8, 6/8, 5/4, etc.

In order to notate a simple blues shuffle rhythm, which is really a 4/4 with 4 main pulses (which the bass player plays), in which the beat is divided into three, must be notated with a 12/8 time signature. This is counter-intuitive, since no blues or jazz player is counting to "12", but to 4, the main pulse. But this is the only way to divide 4 main pulses into 3 parts each, because 12 is divisible by both 2 and 3.


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## mikeh375

Million R is of course correct but alternatively, a competent muso will also understand that when the beat is divided into 4's with a 3,1 sub-division, ie a dotted quaver and a semiquaver and the performance direction indicated is 'swing', a triplet (rather, jazz) feel is required. 
To add to the good answers, another reason for time sig changes can be to define harmonic flow/ rate of change within a piece in order to enhance clarity in the musical thought and in turn (as Edward has said) increase performance comprehension for players (and audience!). Phrase lengths especially can dictate time sigs as does rubato and other expressive tempo marks.


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