Lesson 9: 拍號 (Time Signatures)

Time signatures typically consist of 2 numbers like in a fraction. It is always written after the key signature at the beginning of a piece, and will not be written again unless the time signature changes halfway in the piece (see Lesson 8). There are 3 types of time signatures: simple, compound, and complex. Each type of time signatures will be disccused below.

The two numbers in a simple time signature tell you the following information:

• Top number: how many beats there are in a bar/measure.
• Bottom number: what the value of one beat is, or the beat value.

E.g. Consider the time signature . The bottom number is 4, which means that each beat is a quarter note; the top number is 2, which means that there are 2 quarter notes in each measure. Similarly, the time signature means that there are 3 beats in each measure, and each beat is an eighth note. An important concept in simple time signature is that each beat can be divided into two subdivisions.



The most commonly used simple time signature is . Because it is so commonly used, it is sometimes written as 'C', which denotes 'the common time'.

In the second type of time signatures: compound time signatures, the numbers are read a little differently.

• Top number: how many subdivisions there are in a bar/measure.
• Bottom number: what the value/duration of one subdivision is.

So what is 'one beat' in a compound time signature? In compound time signatures, each beat is divided into three subdivisions (instead of 2 in simple time signatures). In other words, 'one beat' would be 3 times of a subdivided note in a compound time signature. This also implies that in all compound time signatures, the top number should be divisible by 3 (except for cases like 3/4 or 3/8, because technically it is pointless to have only 1 beat per measure). This is how you can distinguish between simple and compound time signatures.

E.g. The time signature means that each subdivision is an eighth note (bottom number), and there are 6 subdivisions in each measure, meaning there are 6/3 = 2 beats per measure. One beat in this time signature would be a dotted quarter note, because it is 3 times of an eighth note. Similarly, the time signature means there are now 9 subdivisions per measure, which means there are 9/3 = 3 beats per measure. Note that in all compound time signatures, 'a beat' will always be a dotted note.

The third type of time signatures, complex time signatures, are a lot less encountered than simple and compound time signatures. It typically involves a prime number (other than 2 and 3) on the top. E.g. 5/4 or 7/4. In these complex time signatures, a measure can be interpreted differently according to the composer. E.g. for the case of 5/4, the 5 beats can be played as 3+2 or 2+3, and in the case of 7/4, a measure can be divided into 4+3 or 2+3+2, etc.

Things to learn in this lesson:

1. What do the numbers in a time signature stand for?
2. Be able to differentiate between simple, compound, and complex time signatures.
3. What are the differences between simple and compound time signatures?