Music Theory Lesson: Time Signatures

In this music theory lesson you will learn about time signatures, one of the key parts of understanding written music.

In music, there are many little details to remember. Some can change rapidly and be quite strange, such as time signatures. Time signatures tell us how many beats are in a measure and how to count them. They even indicate how fast the tempo should go, in some cases. There can be some pretty odd ones, though, so it's necessary to learn, first, what each part of the "fraction" means.

The bottom part of the "fraction" is the type of beat we're counting (which note gets the beat) - for example, if the bottom of the "fraction" is a two, we're counting the half note (because there are two half notes in a measure). If the bottom number is a four, we're counting the quarter notes (four quarter notes to a measure). If the bottom number is an eight, we're counting the eighth notes (eight eighth notes to a measure). These are all built on a 4/4 time system, the maximum number of beats possible. However, this doesn't mean there can't be more than four beats in a measure where four is the bottom number - there can.

The most common meter is 4/4, which means that there are four beats in a measure. There's also 3/4 (three beats in a measure), 2/4 (two beats in a measure), 5/4 (five beats in a measure - Mission: Impossible is written in 5/4), and even 6/4 (six beats in a measure). There's also common time, another way to write 4/4 (it's written as a C in the place of the numbers). Then there's cut time, which is the same as 2/2. This means there are two beats in the measure - and each beat is one half note. This effectively makes the tempo twice as fast. Cut time is written as a C with a line through it.

All of these are the basic "four," or "duplet" meters. This means that there are two eighth notes to each beat the conductor gives. This is not true in all meters, like the compound meters (6/8 is an example). In compound, or "triplet" meters, there are three eighth notes to each beat.

There are three common triplet meters: 6/8, 9/8, and 12/8. 6/8 is two beats of three eighth notes (six eighth notes), 9/8 is three beats of three eighth notes (nine eighth notes), and 12/8 is four beats of three eighth notes (twelve eighth notes). Both 9/8 and 12/8 are commonly used in swing music.

In some cases, composers can even use 7/8, and possibly others, such as 10/8. These would most likely be conducted in eight (so that each eighth note gets its own beat).

There are exceptions to any time signature that a composer can notate. In a duplet meter, the composer can write what is known as "triplets." This is when three notes are used in the place of two. It can be done with eighth notes and quarter notes in any duplet meter, and CAN be done with half notes in a 4/4 or common time meter, but this is unusual. Triplets are played faster than the duplets. If the first note begins on the conductor's beat (eighth notes can begin on the "and" of a beat), it will be the only way to do so. The other two notes must be played before the conductor gets to the third beat.

In a triplet meter, the composer can write duplets. These are slower than the other notes, and are usually written only as eighth notes. Where there are three eighth notes (one beat), they may change to two eighth notes. Again, only the first note will come with the conductor's beat (which would happen anyway, unless the conductor was conducting eighth notes).

Duplets and triplets are notated by being barred differently than the other notes. If they are eighth note triplets in a duplet meter, they will be barred as three eighth notes, whereas most eighth notes are barred in groups of two or four. In a triplet meter when there are eighth note duplets, the reverse will be true. With quarter notes (and sometimes with eighth notes), there will be a bracket under the notes and a small number two or three, indicating whether it is a triplet or a duplet.

Time signatures may change often in a piece - it's possible to change as frequently as every measure! If a time change occurs at the beginning of a line, it will be notated on the line before and at the beginning of the line where the change is in effect. If not, it will be notated at the beginning of the measure. If no time changes occur, the time signature will be marked only once, at the beginning of the piece (the clef appears first, then the key, then the time signature).

Time signatures affect tempo (such as 2/2 being faster than 4/4), but they are not the last word. There may be a quarter note or a dotted quarter note (depending on whether it's a duplet or triplet meter, respectively) at the beginning of the piece which equals a specific number. This number is the number of beats per minute, and it tells the exact tempo. Many pieces don't have this, however. What they usually do have is a word or two at the beginning which indicates what kind of tempo should be taken. Largo, for example, indicates a very slow tempo. Allegro moderato indicates a relatively fast tempo. The descriptions may also be in English, such as "not too fast," or "easy swing tempo."

Time signatures can be tricky to understand sometimes, but are fairly easy to learn. Since they are essential to all musicians, it's good to learn how to count them and why we count them the way we do. One should always remember to ask a teacher or conductor if any questions about the tempo or beats per measure arise.

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