Introduction

Music doesn't always stay at the same tempo, or it could be quite boring! In this guide we'll look at the various ways tempo can change over the course of a piece of music.

Tempo

Before we look at how music can change tempo, it would be a good idea to read through Tempo: fast and slow, so that you are clear about the concept of tempo and what it means.

Half and double

A very straightforward way for a piece of music to change tempo is simply to switch to half-speed (or double-speed).

This can be done in two ways:

• Switching between cut-common (also known as alla breve) and common time
• Using the marking doppio movimento to "double the movement"

Both of these can be used together, as shown in this example, in which the music goes at twice the tempo after the double bar (the counting remains at the same speed):

The tempo doubles at the double bar while the beats remain constant

It is important to note that in these techniques, the beat remains at a constant speed, but that the number of notes in each beat is doubled.

In the example above, there are initially four crotchet beats in the bar (the speed could be, perhaps, crotchet = 100 or 100bpm), and then after the double bar there are two minim beats in the bar. However, the beat stays the same, at 100bpm, meaning that there are now twice as many crotchets per minute (because there are two crotchets to each minim), and so the music sounds twice as fast!

Faster

The tempo can also gradually get faster, rather than suddenly doubling in speed. There are several markings that you will come across that require the player to increase the tempo gradually:

Often, (in particular with accelerando) you will see these markings with a dotted line stretching over the passage in which the acceleration should take place, until a new steady tempo is reached, as in this example:

The tempo gradually gets faster until the double bar

Slower

Just as the tempo can gradually get faster, it can of course gradually get slower. Here are the most common terms:

Just as with the "get faster" marks, a dotted or dashed line is often used over the relevant music, particularly with "rit." markings, until the new tempo is reached.

Flexible time

It is often necessary in music to temporarily suspend a regular tempo, for expressive effect. There are several common terms indicating this kind of tempo change:

Metric modulation

Sometimes, the time signature will change but it might not be obvious how (or even if) the tempo changes. In such cases, it is usual for an extra marking to be added, for clarification.

If the beat length and duration stay the same...

If the time signature changes (e.g., from 2/4 to 3/4), you would see a marking as shown below (simply referred to as "crotchet equals crotchet"):

The crotchet beat remains the same even though the number of beats per bar changes

This marking tells us that a crotchet in the old tempo has the same duration as a crotchet in the new tempo, and in this example, there is not a change in tempo.

In cases like this, you might also see the Italian marking: l'istesso tempo, which means "the same tempo".

If the beat length changes...

Sometimes, the beat length might change but the beat duration remains the same. This is common when going from simple time to compound time (or vice versa), as shown below:

Changing from simple to compound time without changing the tempo

In this case, a crotchet in 2/4 has the same duration as a dotted crotchet in 6/8 - so the beat has the same duration as before, even though its length has changed. In other words, this is also not a change in tempo!

If the beat duration changes...

By contrast, the time signature might remain the same, but the beat length should change by some fixed proportion. This is known as a metric modulation.

In the example below, the music changes from a slow tempo (Adagio) to a faster tempo (Allegro), and the speed changes precisely, such that a quaver in the slow tempo has the same duration as a crotchet in the faster tempo:

Changing from a slow to a faster tempo without changing beat length

Note that in this example, the beat length remains the same, but the beat duration changes - compare this with the previous two examples - this time, there is a change in tempo.

Read more...

With a subscription to Clements Theory you'll be able to read this and dozens of other study guides, along with thousands of practice questions and more! Why not subscribe now?