Creating musical sounds
Creating musical sounds

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Creating musical sounds

2 What is a musical instrument?

Figure 1
(a–c) Peter Seabrook, The Open University; (d) Richard Seaton, The Open University; (e) Courtesy of Bowling Green State University, Ohio; (f) © Getty Images; (g) Courtesy of Yamaha; (h) © Paul Bergen/ Redferns
Figure 1 A selection of musical instruments: (a) violin, (b) trumpet, (c) flute, (d) piano, (e) pipe organ, (f) electric guitar, (g) synthesiser, and (h) voice (Luciano Pavarotti, an opera singer)

What exactly is a musical instrument?

Any sound, whatever it may be, is caused by something vibrating – in other words, by something that is moving back and forth, either in a regular manner or in a random manner, about the position it occupies when at rest. The source of the sound may be a car engine, a burglar alarm or a bird singing. Whatever it is, some part of it must be vibrating for it to produce sound. The vibrating part pushes and pulls against neighbouring air molecules, creating regions of higher pressure called compressions (regions where the air molecules are pushed together) and regions of lower pressure called rarefactions (regions where the air molecules are pulled apart). These compressions and rarefactions travel away from the vibrating source in the form of a longitudinal wave (a sound wave) until they reach the ear, where they are interpreted as sound.

When a musician plays a musical instrument, sound is produced. Therefore, by playing the instrument the musician must be causing it to vibrate. This is our first signpost as to what a musical instrument is. A musical instrument is a sound source and as such at least part of it must be able to vibrate. Note that in this unit I shall be talking only about acoustic musical instruments, so when I mention a musical instrument you should assume I am talking about such an instrument rather than an electronic instrument. However, even electronic instruments ‘vibrate’ in some way to produce sound, but in this case the vibrations are in the form of electrical voltage variations and the sound is produced by feeding these voltage variations through an amplifier to a loudspeaker.

So, what sets a musical instrument apart from, say, a barking dog or waves breaking on a beach? These two things produce sound but you wouldn't consider them to be musical instruments. Is it that a musical instrument is able to produce sounds of different pitches? Instruments such as the violin, flute and trumpet can certainly do so. Consequently, these instruments can be used to play melodies or tunes. However, what about percussion instruments such as maracas or castanets (Figure 2)? The sound produced when maracas are shaken resembles the noise produced by your television set when you pull the aerial lead out or the noise produced by water rushing down a waterfall (this type of hissing noise is often called white noise). Castanets, on the other hand, produce sharp clicks when struck together. Neither of these two sounds has a discernible pitch and yet we refer to maracas and castanets as musical instruments. They emphasise the rhythmic structure in a piece of music rather than providing the melody. It is clear, then, that the ability to produce pitched notes is not the thing that distinguishes a musical instrument.

Figure 2
(a) © Getty Images; (b) Peter Seabrook, The Open University ©
(a) © Getty Images; (b) Peter Seabrook, The Open University
Figure 2 Percussion instruments: (a) a pair of maracas; (b) a pair of castanets

So, what does characterise a musical instrument? Well, what we really want from a musical instrument is to be able to use it to produce sounds in a controlled and predictable manner. Both our pitched instruments (violin, flute, trumpet) and our unpitched instruments (maracas, castanets) satisfy this criterion. A barking dog and breaking waves do not satisfy the criterion because neither produce sounds in a predictable manner nor can the production of the sounds be humanly controlled. What about a vacuum cleaner? Could it be classed as a musical instrument? Well, it can be controlled by a human and can produce sound in a predictable manner, so according to our criterion it could be used as a musical instrument. Indeed, three vacuum cleaners are employed (along with an electric floor polisher and several rifles!) in Malcolm Arnold's ‘A Grand, Grand Overture’, a piece composed for the 1956 Hoffnung Music Festival (see Box 1).

Box 1: Hoffnung Music Festivals

Gerard Hoffnung (1925–1959) (Figure 3) was a man of many talents. He originally came to prominence as a cartoonist (see Figure 4), and was particularly renowned for his caricatures of musicians. However, he was also a teacher, a humorist, a well-respected broadcaster and raconteur, and a musician. Although he died at the early age of thirty-four, he left behind a wealth of sketches, cartoons, ideas and the Hoffnung Music Festivals.

Figure 3
© The Hoffnung Partnership, London ©
© The Hoffnung Partnership, London
Figure 3 Gerard Hoffnung
Figure 4
© The Hoffnung Partnership, London ©
© The Hoffnung Partnership, London
Figure 4 Hoffnung cartoon featuring the ‘Vacuum Quartet’

In the mid-1950s, Hoffnung decided to translate some of his musical cartoons on to the concert stage. Leading composers were commissioned to write humorous compositions, and top conductors, soloists and musicians were enlisted. The result was the first Hoffnung Music Festival held on 13 November 1956 at London's Royal Festival Hall (Figure 5). The concert proved a huge success, providing an evening of fun, laughter and musical caricature.

Such was the popularity of the first concert that a second was staged in 1958 and a third followed in 1961 after Hoffnung's death. Since those performances over forty years ago, internationally famous orchestras have continued to present items from the Hoffnung repertoire to packed audiences.

Figure 5
The Hoffnung Music Festival Concert 1956, designed by Gerard Hoffnung © Gerard Hoffnung ©
The Hoffnung Music Festival Concert 1956, designed by Gerard Hoffnung © Gerard Hoffnung
Figure 5 Programme cover of the 1956 Hoffnung Music Festival concert

Activity 1

The audio track below contains a short section from ‘A Grand, Grand Overture’ for you to listen to. You should be able to hear the vacuum cleaners around 45 seconds into the track, with the rifles following about 5 seconds later.

Click 'Play' to listen to Audio Clip 1

Download this audio clip.Audio player: ta212_2_001s.mp3
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We can now be a little bit more precise in defining what constitutes a musical instrument. A musical instrument is a sound source with a predictable output that can be controlled by a player.

Activity 2

Discuss which of the following could be classed as a musical instrument according to the definition above:

  1. a miaowing cat;

  2. a flute;

  3. breaking glass;

  4. an anvil with hammer;

  5. a car engine.


  1. The miaowing of a cat can't be classed as a musical instrument. It is neither predictable nor controllable by a human.

  2. A flute can be classed as a musical instrument. Its output is predictable and controllable by a human.

  3. Breaking glass could possibly be classed as a musical instrument. Although it can be controlled by a human, the sound produced may have a degree of unpredictability.

  4. An anvil struck with a hammer can be classed as a musical instrument. A human can strike an anvil in a controlled manner and the sound produced is predictable. Indeed, an anvil is used as a percussion instrument in Verdi's ‘Anvil Chorus’ and in Wagner's ‘Ring’ for the forging of the ring.

  5. A car engine can be classed as a musical instrument. The revving of a car engine can be controlled by a human and the output is predictable.

Before we finish this section, I should just add the comment that modern technology allows us to digitally sample any sound and play it back via a keyboard in a controlled and repeatable manner. In this way, a cat's miaows can be turned into the notes of a piece of music. However, it is important to note that the cat is not the musical instrument. The electronic keyboard with the stored sample of the cat's miaow is the instrument.


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