Time signatures, and what 4/2 means
A time signature is two numbers stacked. You already read the top one by instinct: it's how many beats are in a bar. The bottom one is the part that trips people up, because it isn't a count at all. It names which note value gets one beat.
| Bottom number | One beat is a… | Because |
|---|---|---|
| 1 | whole note | a whole |
| 2 | half note | half of a whole |
| 4 | quarter note | a quarter of a whole |
| 8 | eighth note | an eighth of a whole |
So everything you already know (3/4, 4/4, 5/4) has a 4 on the bottom, which means the quarter note is the beat. Three, four or five quarter-note beats per bar.
4/2
Same idea, different unit: four beats per bar, and each beat is a half note. A full bar holds four half notes, which is the same amount of written time as eight quarter notes.
Does it sound slower?
No, and this is the bit that clicks it into place. How fast the music goes is set by the tempo, not the time signature. The tempo marking tells you how many beats per minute, whatever note the beat happens to be. Four half-note beats at 80 per minute sound exactly like four quarter-note beats at 80 per minute. You count "1, 2, 3, 4" at the same speed either way.
What changes is the writing. In 4/2, the notes that sound like quarter notes are written as half notes, the ones that sound like eighths are written as quarters, and so on. Everything is one size bigger on the page.
Then why bother?
- Tradition. Church music and Renaissance choral music were written with the half note (or larger) as the pulse, and hymnals still often use 4/2 or 3/2.
- The look of the line. Long, broad notes read as calm and sustained. A slow hymn in 4/2 looks like what it sounds like.
- Cleaner fast notes. In a busy passage, what would be sixteenths in 4/4 become eighths in 4/2: fewer beams, easier to read.
Hear it
Pick one. The strong beat of each bar is the higher click. 4/4 and 4/2 are set to the same beats per minute so you can hear that they're identical. 2/2 and 6/8 are there because they're the two you'll meet next.
The two you'll meet next
2/2, "cut time". Two half-note beats per bar, often written as a C with a line through it. Same bar length as 4/4, but you feel two big steps instead of four. Marches and fast show tunes live here: written like 4/4, felt in two.
6/8. This one breaks the rule a little. On paper it's six eighth notes per bar, but at any normal speed you feel two beats, each split into three: ONE-two-three TWO-two-three. Signatures with 6, 9 or 12 on top are called compound, and their beat is three of the bottom note. That's the lilt in a jig or "House of the Rising Sun".
The one-line version
Top number: how many beats in a bar. Bottom number: which note counts as one beat. The tempo decides how fast it goes. So 42 is four beats a bar, each written as a half note, and it can be just as fast as 4/4.