Meter involves the way multiple pulse layers work together to organize music in time. Standard meters in Western music can be classified into *simple meters* and *compound meters*, as well as *duple*, *triple*, and *quadruple* meters.

Duple, triple, and quadruple classifications result from the relationship between the counting pulse (Karpinski's *secondary* pulse) and the pulses that are *slower* than the counting pulse (Karpinski's *primary* pulse). In other words, it is a question of *grouping*: how many beats (secondary pulse) occur in each bar (primary pulse). If counting-pulse beats group into twos, we have duple meter; groups of three, triple meter; groups of four, quadruple meter. Conducting patterns are determined based on these classifications.

Simple and compound classifications result from the relationship between the counting pulse and the pulses that are *faster* than the counting pulse. In other words, it is a question of *division*: does each beat divide into two equal parts, or three equal parts. Meters that divide the beat into two equal parts are *simple meters*; meters that divide the beat into three equal parts are *compound meters*.

Thus, there are six types of standard meter in Western music:

- simple duple (beats group into two, divide into two)
- simple triple (beats group into three, divide into two)
- simple quadruple (beats group into four, divide into two)
- compound duple (beats group into two, divide into three)
- compound triple (beats group into three, divide into three)
- compound quadruple (beats group into four, divide into three)

In a time signature, the *top number* (and the top number only!) describes the type of meter. Following are the top numbers that always correspond to each type of meter:

- simple duple: 2
- simple triple: 3
- simple quadruple: 4
- compound duple: 6
- compound triple: 9
- compound quadruple: 12

In *simple meters*, the bottom number of the time signature corresponds to the type of note corresponding to *a single beat*. If a simple meter is notated such that each quarter note corresponds to a beat, the bottom number of the time signature is 4. If a simple meter is notated such that each half note corresponds to a beat, the bottom number of the time signature is 2. If a simple meter is notated such that each eighth note corresponds to a beat, the bottom number of the time signature is 8. And so on.

In *compound meters*, the bottom number of the time signature corresponds to the type of note corresponding to *a single division of the beat*. If a compound meter is notated such that each dotted-quarter note corresponds to a beat, the eighth note is the division of the beat, and thus the bottom number of the time signature is 8. If a compound meter is notated such that each dotted-half note corresponds to a beat, the quarter note is the division of the beat, and thus the bottom number of the time signature is 4. Note that because the beat is divided into three in a compound meter, the beat is always three times as long as the division note, and *the beat is always dotted*.