Music Lessons

Timbre and classification of musical instruments

Italian flag
Leggi in Italiano

Timbre is that quality of sound that allows us to identify a sound source and distinguish it from any other. Unlike pitch and loudness, timbre cannot be measured on a scale and is difficult to define, so much so that people often resort to the even more confusing expression ‘colour of sound’. So let’s try to better understand what timbre is, what it depends on and how musical instruments are classified.

Definition of timbre

To begin with, listen to this sound.

Surely you recognised the instrument that produced it: the piano. You recognised the timbre of a piano. So here is a first definition: timbre allows us to recognise a sound source and identify it. Now let’s try some other instruments, try to recognise the timbre of these as well.

These three sounds are similar, but the first has the timbre of piano, the second of organ, the third of string instruments. Surely you recognised different timbres and were able to connect them to a specific instrument: piano, organ, string instruments. How was this possible? How does our ear recognise different instruments?

To begin with, let us analyse the phenomenon of timbre from a scientific point of view.

Timbre in acoustic physics

When a musical instrument produces a sound, along with the fundamental note it also generates higher frequency sounds, called harmonic sounds. The timbre of an instrument is determined by the spectral composition of the sound it emits.

The spectrum of sound produced by different instruments varies due to the different distribution of energy between the fundamental note and the upper harmonics. Put simply, the timbre of the instrument varies according to the quantity and quality of the harmonics.

The timbre of an instrument is therefore largely due to the waveform of the sound it emits, which in turn depends on harmonic sounds.

A graphic representation of timbre: the harmonic formant

Un esempo di formante armonica, la rappresentazione grafica del timbro. Disegno di Andro Cecovini

The diagram shows how the various notes enter into resonance when the fundamental note is played. In this case, the root note is C, so E and G are particularly stressed, but the other notes also resonate. The values of these resonances vary from instrument to instrument and voice to voice, determining the timbre. This graph has been drawn as an example; each instrument would provide an individual and unique graph.

*Thanks for this paragraph to Andro Cecovini, a kind visitor who proposed this useful contribution

This is a summary of the scientific explanation of the phenomenon. However, we know that music has a very particular point of view, which does not always coincide with that of acoustic physics.

The timbre in musical instruments

In the case of musical instruments, timbre is determined by the material of the musical instrument and how the sound is produced. For example, we recognise the violin and the cello as similar, because they are both stringed instruments made of wood and strings, which produce sound by rubbing the strings together.

In the guitar, too, the sound is produced by the vibration of the strings, but these are plucked directly by the hand and not rubbed with a bow. Although they are both stringed instruments, the violin and guitar have a very different timbre. The piano is also a stringed instrument. In the piano, however, the strings are struck by hammers operated by the keyboard.

Listening to a piano, a guitar and a violin, we clearly recognise the sound of each. The sound of a saxophone is even more distant and certainly a piano resembles a guitar more than a saxophone. In the saxophone there are in fact no strings, the sound is produced by the vibration of the reed and the air compressed into the instrument.

Let us now look at two different ways of classifying musical instruments, according to how the instrument is played, or according to the actual sound source. Both affect timbre.

Classification of musical instruments

Musical instruments are classified in two different ways, depending on the point of view. A first classification is based on how the instrument is played, and the section it occupies in the orchestra. From this perspective, instruments are classified in this way:

  • Bowed string instruments
  • Wind instruments
  • Keyboard instruments
  • Percussion instruments

This classification is logical and easy to understand. A string instrument is played with the bow, wind instruments are played by blowing into the instrument, keyboard instruments by pressing keys with the fingers. However, this system is not as accurate as it seems, because it does not take into account the actual sound source.

For example, organ and piano are keyboard instruments, but in the organ the sound is produced by the air inside the pipes, while in the piano there are strings that are struck by a hammer. This is why there is an even more accurate classification of instruments that is focused on how the sound is actually produced. We therefore distinguish:

  • Chordophone instruments, in which the sound is produced by the vibration of strings. Both the piano and the guitar or the bowed strings are chordophones.
  • Idiophone instruments, in which the entire body of the instrument vibrates. Many percussion instruments are idiophones, e.g. the triangle, marimba, cymbals.
  • Aerophonic instruments, in which the sound is derived from the vibration of air in the instrument. Flute, clarinet, saxophone, trumpets and trombones belong to this category. However, some of these instruments are called ‘woodwinds’ because the sound comes from the vibration of a reed, which is also made of wood even in metal instruments such as the saxophone.
  • Membranophonic instruments, in which the sound is produced by the vibration of a membrane. Drums of all types belong to this category.

The timbre of musical instruments thus depends on many things, not only on the actual source of the sound but also on the way the musician interacts with the instrument. Let us now analyse the most common instrument of all: the voice.

The human voice

Whether we know the conformation of a musical instrument or not, if we have heard a trumpet or a piano at least once, we will also be able to recognise them in the future. In the same way, we can recognise and distinguish people we know, simply by listening to their voice.

Different human voices also have different timbres, in which case the timbre is dictated by the conformation of the vocal cords and the phonatory apparatus as a whole (larynx, palate, nose, etc.). Furthermore, even if we do not know a person, we are usually able to recognise a male voice from a female voice or that of an elderly person from that of a child.

In music, voices are classified into six categories: soprano, mezzo soprano, alto, tenor, baritone, bass. The first three refer to female voices, the last three to male voices. The classification is based on the singer’s vocal register, i.e. his or her ability to sing high or low notes.

Soprano and tenor are the highest vocal registers, mezzo soprano and baritone are the intermediate vocal registers, alto and bass are the lowest vocal registers. Here is a table summarising the classification of male and female voices.

High registerMedium registerLow register
Female voiceSopranoMezzo sopranoAlto
Male voiceTenorBaritonBass

Although the most appreciated singers are often those capable of performing in the high register, and thus sopranos (among women) and tenors (among men), the rarest voices are those in the low register: alto and bass. Those with a voice in the lower register, whether male or female, would be well received in a choir, where the shortage of basses and altos is chronic, while sopranos and tenors abound!

In our lives, we listen to thousands of voices and therefore our ear is highly trained in recognising human voices. However, an ordinary person is not as used to recognising small nuances in the timbre of a musical instrument, whereas a musician’s ear is used to recognising small differences between instruments that may escape a less trained ear.

Qualità del suono timbro

The differences between instruments of the same type. Every musician has ‘his’ timbre

While the difference between the timbre of a guitar and a violin is easy to recognise, even for non-musicians, it is not so easy to recognise the difference in timbre of two guitars or two violins. All acoustic instruments have small differences in timbre from one another, but these differences can escape most people.

A saxophone player notices the difference in the timbre of his saxophone if he changes the mouthpiece, which is only one part of the instrument. Similarly, a violinist recognises the state of wear on the strings of his instrument. This proves to us how sophisticated the human ear is and how it can be educated to recognise almost imperceptible nuances of timbre.

A pianist can immediately recognise the difference between a grand piano and an upright, as well as that between a Steinway piano and a Yamaha, to mention two very famous brands. However, there is another element that greatly conditions the timbre of an instrument: the performer.

The timbre of an instrument is also determined by the musician playing it; the same instrument played by two different people sounds different.

In the case of a wind instrument, the difference depends on the mouthpiece and the way the air is emitted; for the piano, it depends on the weight and gesture of the hand, but also on the way the sounds are connected to each other. In any case, each musician, especially if he or she is experienced, has his or her own very particular sound, different from what other musicians have, even though they play the same instrument.

Conclusions. Timbre is not measurable

Timbre is the most mysterious component of music, even from a scientific point of view there are some things that are inexplicable: for example, why a Stradivarius violin has such a special sound that is difficult to imitate.

Using a visual metaphor, timbre is often referred to as the ‘colour of sound’. This definition can help us describe this elusive quality of sound, however, any juxtaposition between hearing and seeing is partial and arbitrary. Music is in fact the most abstract of the arts and many aspects of music are difficult to define.

Timbre in particular is impossible to place on a scale. Sometimes we talk about timbre being darker or lighter, but many times we refer to pitch rather than actual timbre, thus confusing two distinct qualities of sound: pitch and timbre.

Finally, while science investigates phenomena, including acoustic ones, with the aim of fully understanding them, for a musician timbre is just an element, a part of music. Surely it matters much more how timbre relates to another, even more abstract and indefinable characteristic: interpretation.

In the end, what matters most in music is the result. There are singers who are slightly out of tune, yet are considered great masters. Similarly, there are pianists who have a rough and harsh sound, e.g. Thelonious Monk among jazz pianists, who nevertheless manage to move us and express music of great tenderness and sweetness.

Music is not an exact science, far from it. Trying to fully understand it should not replace the main pleasure: enjoying music, as a listener and as a performer. The goal of music is happiness, not perfection.

As usual, I would love to hear your opinion about this lesson: is there something important about timbre that I have forgotten and you would like to add? Write your thoughts or questions in the comments to the lesson. Thank you!

Do you want to receive my free lessons?

Sheet music, harmony lessons, music theory and musical analysis.