Time Signatures and Meter Types

A time signature looks like a fraction but doesn't act like one. The bottom number tells you which note value counts as one unit: 4 means quarter note, 8 means eighth note, 2 means half note. The top number tells you how many of those units fill a measure. You never reduce 6/8 to 3/4 the way you'd reduce a fraction, because the bottom number is naming a specific note, not a denominator you can scale freely. Change the bottom number and you change what kind of note is doing the counting, even if the math looks equivalent.

Meter type comes from two separate questions layered on top of the numbers. First, how many beats per measure: two is duple, three is triple, four is quadruple. Second, how each beat divides naturally: into two equal parts is simple, into three equal parts is compound. Simple time signatures have a top number of 2, 3, or 4, and the bottom number names the beat directly. Compound time signatures have a top number that's a multiple of 3, like 6, 9, or 12, and the bottom number names the division, not the beat; you have to group those divisions into threes to find the real beat. So 6/8 isn't six beats, it's two beats, each made of three eighth notes: duple compound.

This sits right after key signatures because both are notation shortcuts: one fixes pitch collection, the other fixes the beat grid, and together they tell you everything you need before a single note sounds. Meter type also sets up how you'll later read syncopation and hypermeter, since those depend on knowing where the real, felt beats land.