Related
One question is enough to sort the three types:
Can each beat be split into two?
| Type | Beat divided into | Test | Examples |
|---|---|---|---|
| simple | two | numerator not a multiple of 3 (or denominator 4 / 2) | 2/4, 3/4, 4/4 |
| compound | three | numerator a multiple of 3, denominator ≥ 8 | 6/8, 9/8, 12/8 |
| irregular | — | numerator 5, 7 or similar | 5/4, 7/8 |
One easily missed detail: 6/4 is also compound (6 = 3 × 2), so "denominator ≥ 8" is an extra condition distinguishing patterns like 6/8 from 6/4, which is usually felt as two large beats. The reliable test remains listening: does each beat divide in two or in three?
What actually separates 6/8 from 3/4
The most practical distinction in this entry:
| 3/4 | 6/8 | |
|---|---|---|
| Beats | three | six (or two large beats) |
| Beat divided into | two | three |
| Impression | one accent per beat, three in all | pairs of beats, two groups in all |
| Typical genres | waltz, march | lullaby, barcarolle, many folk dances |
The point: this is not a matter of speed but of how each beat divides. Playing 3/4 faster does not make it 6/8, and playing 6/8 slower does not make it 3/4.
Irregular metre: grouping decides the sound
5/4 and 7/8 are incomplete on their own — they must be given a grouping:
| Signature | Grouping | Impression |
|---|---|---|
| 5/4 | 3+2 | like "a bar of three plus a bar of two" (the Neapolitan dance pattern) |
| 5/4 | 2+3 | two then three, accent first, more square |
| 7/8 | 2+2+3 | the classic Balkan folk grouping |
The same notes regrouped become a different piece, because the accent cycle changes (see metric accent). It also explains why irregular metre "sounds modern": the unsettling effect comes not from dissonance but from being unable to count.
Its relation to tuplets
A boundary that is easily confused: three notes inside a compound beat need no tuplet marking (the denominator already is 8 or 16), whereas three inside a simple beat require a triplet (see tuplet).
A one-line test: is the three written into the time signature? Yes → compound metre (no tuplet needed); no → simple metre (a triplet is required).
Diagram: the inner structure of the three types
Listen: two large beats versus three
Use rhythm to compare 6/8 (six eighths felt as two large beats) with 3/4 (three quarters). Count how long it takes the main accent to return — in 6/8 it is one group of three out of two groups; in 3/4 it is every beat, three times.
Common misconceptions
- "6/8 is just 3/4 played faster." Not a matter of speed but of how the beat divides. They are two
- "Any numerator divisible by 3 is compound." The denominator matters too: 6/4 is usually felt as two large
- "5/4 is merely rare." It is incomplete without a grouping (3+2 or 2+3), and different groupings are
- "The threes in compound metre are triplets." They are not (see tuplet). The three is
different classes of metre.
beats, and the real test is hearing how the beat divides.
different pieces.
written into the signature, so no tuplet marking is needed. :::
Listen in the library
All tracks from midicn-lib — inline badge is the license tier (C1 commercial / C2 non-commercial / C3 study only).
Sources
- 单拍子（每拍二等分）/ 复拍子（每拍三等分，分子为 3 的倍数）/ 混合拍子（不规则组合）的分类，属乐理通则
- 5/4 与 7/8 的重音分组（2+3 或 3+2）决定听感，为通行表述
Used for fact-checking only; all prose is original.