Time signature
The two numbers stacked at the start of the staff sum up the measure: how many beats it has and which note value takes one beat. Here you learn to read them in simple meters, to decode them in compound meters, where they mislead at first, and to recognise the C and cut-C signs.
At the start of the staff, right after the clef and the key signature, there are usually two stacked numbers. They are the time signature, and they say at once what the two previous topics explained: how many beats there are in each measure and which note value takes one beat (Lacerda 1966, ch. VIII).
The time signature is written once, at the beginning, and holds until the end of the music or until another one appears (Med 1996, ch. XIX). In English it is read "three-four". Portuguese reads it with "por", "três por quatro", and Lacerda insists on it: "nove por oito", never "nove oitavos", nine eighths.
The lower number is a note value
The lower number says which note value is being counted. Each value gets the number of times it fits in a whole note:
| Number | Note value |
|---|---|
| 1 | whole note |
| 2 | half note |
| 4 | quarter note |
| 8 | eighth note |
| 16 | sixteenth note |
| 32 | thirty-second note |
| 64 | sixty-fourth note |
That is why a time signature looks like a fraction. Lacerda explains that it really is a fraction of the whole note: two-four is two quarters of a whole note, that is, two quarter notes per measure (Lacerda 1966, ch. VIII). On the staff, though, it carries no fraction bar, which would fall on the third line (Med 1996, ch. XIX).
In simple meter, it reads directly
In simple meter, the upper number is the number of beats, and the lower one is the beat unit.
Two-four: two beats, each beat a quarter note.
Four-four: four quarter-note beats.
Two-two: two beats, and now each beat is a half note.
Lacerda lists the upper numbers of simple meters: 2, 3, 4, 5 or 7, the same beat counts as in the topic on the measure.
In compound meter, it misleads
In compound meter the beat unit is dotted, and a dotted value has no number to stand for it. Notation's way out is to count the division instead of the beat: the lower number becomes the value the beat divides into, and the upper one, how many of those fill the measure (Lacerda 1966, ch. VIII).
Six-eight seems to say "six eighth-note beats". It does not. It is six eighths per measure, grouped in threes: two beats, each a dotted quarter. That is what the beams show in the second measure.
To get from the signature to the real meter, the sum is this:
- beats: the upper number divided by 3. Six-eight has 6 ÷ 3 = 2 beats.
- beat unit: the lower number's value, one step longer, with a dot. Eight is an eighth; one step longer is a quarter; dotted, a dotted quarter.
Nine-eight: 9 ÷ 3 = 3 dotted-quarter beats. Twelve-eight would be four. So in compound meters the upper number is always a multiple of three: Lacerda gives 6, 9, 12, 15 and 21.
From one to the other
A simple and a compound meter correspond when they have the same number of beats and the same note as beat unit, undotted in one and dotted in the other. Lacerda gives the sum to move between them straight from the signature: from simple to compound, multiply the upper number by 3 and the lower by 2; from compound to simple, divide (Lacerda 1966, ch. VIII).
| Simple | × 3 above, × 2 below | Corresponding compound |
|---|---|---|
| 2/4 | 2 × 3 = 6, 4 × 2 = 8 | 6/8 |
| 3/4 | 3 × 3 = 9, 4 × 2 = 8 | 9/8 |
| 4/4 | 4 × 3 = 12, 4 × 2 = 8 | 12/8 |
| 2/2 | 2 × 3 = 6, 2 × 2 = 4 | 6/4 |
C and cut C
Two time signatures have a sign of their own instead of numbers. C stands for four-four, and English calls it common time:
Cut C, crossed by a vertical stroke, stands for two-two, and is also called cut time or alla breve:
Blatter explains that both signs are remnants of an older way of indicating time (Blatter 2007, part 1, art. 4). Med tells where they come from: in the old notation a circle meant triple meter, considered perfect; a half circle, which looks like a C, meant quadruple; and a crossed half circle meant duple, both considered imperfect (Med 1996, ch. XIX). So the C is not the initial of "common", even though the English name suggests it.
The same music, different signatures
A time signature is a choice of notation. Blatter shows that the same rhythm can be written in two-four, in two-two or in eighth notes, and sound exactly the same, as long as the tempo follows the change of note value (Blatter 2007, part 1, art. 4).
Both have two beats per measure and the same rhythmic shape; in the second, every value has doubled. The player here keeps the quarter note at one fixed speed, so it plays the second more slowly. With the half note taking the quarter's place as the pulse, the two would be identical.
What comes next
With the signature read, every measure has its beats counted. But they do not all weigh the same: the first beat usually sounds stronger than the rest. That is the subject of metric accent.
References
- Blatter, Alfred. 2007. Revisiting music theory: a guide to the practice. New York: Routledge.Consulted: part 1, art. 4
- Lacerda, Osvaldo. 1966. Compêndio de teoria elementar da música. 3rd ed. São Paulo: Ricordi Brasileira.Consulted: ch. VIII
- Med, Bohumil. 1996. Teoria da música. 4th ed. Brasília: Musimed.Consulted: ch. XIX