Introduction

Metre is the fundamental reference point for the organisation of time in most music.  As we have seen, metre is best defined as the relationship of at least two pulses where the slower pulse is included in the faster pulse.  The inclusion relationship usually involves a multiple of two (duple) or three (triple).  Two inclusion-related pulses give us a minimal metre and three or more give us a deep metre.

A more limited concept of metre, however, may also relate to common practices of the notation of time in music—the time signature and the use of bars and bar lines. These elements can be a reliable indicator of metre in most music, in fact they often are.  However, they only describe part of the metrical properties of any piece of music and sometimes can be misleading.

A terminological clarification

While is it common in many texts to use the term “metre” in combination with the terms we we outline below, as in “simple triple metre” or “compound duple metre,” and so on, we prefer to replace the word “metre” with “time” in this instance, to avoid confusion with the broader definition of metre as stated above.  So, we will talk in terms of “simple triple time” or “compound duple time,” and so on.

Components of time signatures

Most time signatures in common practice music involve two components: the time signature itself, which is a pair of vertically stacked numbers present at the beginning of a piece of music, shown immediately after the clef(s) and key signature and the use of bar lines to indicate the boundary between bars of music, in accordance with the time signature.  A simple is shown in Example 1.

When writing time signatures, please note the following:

• From the left line on the staff, the order of symbols is: (1) clef, (2) key signature, (3) time signature
• The time signature spans the staff exactly, the upper numeral touching the third and fifth lines, the lower numeral touching the first and third lines
• The time signature is shown on all staves in a group of staves
• Unlike clefs and key signatures, the time signature is only shown on the first staff, group or system, not on subsequent ones.

time signatures in common use

In common practice, Western music adopts a rather limited number of time signatures, which fall into two categories: simple time and compound time.  Within each category, there are typically three types, according to a basic division of the bar into two (duple), three (triple) or four (quadruple).  Simple time makes its primary beat subdivision into two, compound time makes its primary beat subdivision into three.  (Example 1 is an instance of music in simple duple time.)

The two numbers in each time signature provide information about how many beats there are per bar and the value of these beats.  In speaking about them, we often refer to them by naming the two numbers. For example, we might describe as “three-four” time or as “nine-eight” time.

Note that these two numerals do not form a fraction.  However, when we write them in text, a slash is commonly used: For example, can be written in text as “3/4”; however, avoid writing it like a fraction, as in or ¾.

Simple time

The information provided in simple time signatures is quite straightforward. All information relates to the primary beat level (which is often also the tactus):

The upper number shows how many primary beats there are per bar, typically 2, 3 or 4.

The lower number shows the value of these beats, most commonly 2 (minims), 4 (crotchets) or 8 (quavers)

Compound time

The information provided in compound time signatures is a little more opaque. Because the primary beat in a compound metre will divide into three, rather than two, the primary beat value will be a dotted value. For this reason, the value of the first subdivision is given as the lower numeral. Usually this is will be 8 (quavers), but might also be 4 (crotchets) or 16 (semi-quavers).  This value is almost never the tactus.

This all means that the upper numeral will not indicate how many primary beats there are in a bar.  To determine this, the value has to be divided by three.

• An upper numeral of 6 indicates duple time (6 ÷ 3 = 2)
• An upper numeral of 9 indicates triple time (9 ÷ 3 = 3)
• An upper numeral of 12 indicates quadruple time (12 ÷ 3 = 4)

Abbreviated Time Signatures

There are two symbols in common use as abbreviations.  These are:

• 𝄴 which stands for , also known as “common time”
• 𝄵 which stands for , also known as “cut common time” or “alla breve”

Changes of time signature

The time signature may be changed during the course of a piece of music.  There are a few conventions to be aware of in such cases:

• The new time signature appears immediately after the bar line before the change
• Sometimes, a double bar is used before a time signature change, but this is not compulsory and is more common in older scores and notational practices
• If the change of time signature occurs across a line break, a “courtesy” time signature is placed a the end of the system after the final bar line as well as at the start of the next line
• In a system comprising more than one staff, the rules above apply to all staves in the system