Meters are notated at the beginning of a musical composition with a time signature, two numbers on top of each other that look like a fraction: for example, 2/4, 3/4, 4/4.
Meters can be simple, compound or complex. The meter is compound when the lower number is larger than, as well as divisible by, three: for example, the lower number is 6, 9 or 12. The meter is simple when the upper number is an even number not divisible by three, such as two, four or eight. 3/4-time is also simple time, since the top number is not larger than the number three. Complex meters occur in compositions where each measure is a combination of several other meters.
Note values are written in relation to each other, if a quarter note is the beat then the duration of four beats is a whole note. If an eighth note is the beat, the duration of four beats is a half note. Simple and compound meter refers to the division of the beat. In simple meter, the beat is subdivided into two parts. If the quarter note receives the beat, as in 2/4-time, the two-part subdivision of the beat will be the eighth note, since two eighth notes equal the same duration as a quarter note. In compound time, the beat is subdivided into three parts. Compound meter uses dotted notes to indicate the beat, which increases the duration of the note by 50 percent.
Classification of meters can also be according to the number of beats per measure. For example, duple meter has two or four beats per measure and triple meter has three beats per measure.
In simple meter, the top number is the number of beats per measure and the bottom number represents the note that gets the beat. 2/4-time is simple duple meter as it has two beats per measure, with the quarter note getting the beat. 3/4-time is simple triple meter as it has three beats per measure, with the quarter note getting the beat.
Compound meter is less simple. The top number, divided by three, gives the number of beats in the measure and the bottom number gives the division of the beat, but does not represent the note that gets the beat. For example, 6/8-time is compound duple meter with two beats per measure and 9/8-time is compound triple meter with three beats per measure. In 6/8-time and 9/8- time, each beat is also equal to three eighth notes and the note that receives the beat is the dotted quarter note. As a dotted note value is equal to three of the next smaller note value, a dotted quarter note is equal to three eighth notes.