Timbre
Timbre (TAM-bur) describes the quality of a sound. In terms of everyday life, it is timbre that allows us to recognize voices on the phone. By recognizing characteristics such as smoothness, nasalness, or tenseness in each person's voice, we instinctively identify familiar voices. When it comes to music, timbre allows us to tell the difference between two instruments that are playing the same pitch at the same volume. Timbre is affected by the size and shape of the instrument, the material from which it is made, and the playing techniques that are used to make sounds. Vocal timbre is mostly determined by a person's physical characteristics such as their gender, height, lung capacity, thickness and length of vocal chords, but can also be affected by age, illness, or lifestyle (smoking, for example). Timbre also is very closely linked with the harmonic series, so we will begin there.
Harmonic Series
Every tone (sustained pitch) is actually a composite of several different pitches. These 'extra' pitches, called overtones, are resonant frequencies occurring above the main pitch, called the fundamental. Most overtones are harmonics, which are simple fractional vibrations of the fundamental pitch (1/2, 1/3, 1/4, and so on). Since dividing a string in half causes it to vibrate twice as fast, the frequencies of harmonics can found by multiplying the frequency of the fundamental pitch by 2, 3, 4, and so on.
Note that the first three intervals created by successive pitches in the harmonic series are an octave, a perfect fifth, and a perfect fourth. This is one of the reasons that these intervals are called the 'perfect' intervals. For more on the harmonic series and its implications for harmony and tuning systems, see harmonic series revisited.
The harmonic series affects timbre because each type of instrument produces a distinctive pattern of loud and soft overtones. As we move farther from the fundamental pitch, overtones have a tendency to become more quiet, but on some instruments particular overtones are more or less powerful than this tendency suggests. The graphs below are frequency power spectrums that show the strengths of the first eight harmonics of a D (294 Hz) at the same volume on a flute and on a violin.
strengths of the first eight harmonics on a flute and a violin
(frequency power spectrums of D at 294 Hz)
The first two harmonics on the flute are very strong, but the remaining harmonics are quite weak. This is what gives the flute its characteristic pure timbre. On the violin, the second harmonic is much weaker than the flute's second harmonic, but the 3rd through 8th harmonics are much stronger than the flute's. This pattern makes the timbre of the violin sound much more complex and rich than that of the flute.
Range and Register
Sounding Ranges for Various Instruments
The range of an instrument or voice consists of the highest and lowest pitch it can reach and all the pitches in between. Here you can see the approximate ranges in notation for several different instruments and the four standard vocal parts (we will cover instruments and voice types in more detail in the next two sections). Note that 8va means that the written note should be played one octave higher, 15ma means two octaves higher, and 15mb means two octaves lower.
Sounding Ranges for Standard Voice Parts
The ranges of individual instruments and voices are divided into smaller sections called registers. Sometimes these designations are generic, such as low, middle, or high register, but other times they have special names that come from the history of the instrument or the performance techniques used in that range. For example, the clarinet has a low register which is called the chalumeau (sha-lu-mo) register, after its immediate ancestor. Above the chalumeau register is the clarion or clarino range, which is named for its clarity and trumpet-like timbre, and above that is the altissimo register, named simply with the Italian word for 'very high'.
As instruments and voices move between these registers, there are subtle changes in timbre. Returning again to the clarinet, the chalumeau register is known for being rich, full, and dark, whereas the clarino register is described as bright and clear and the altissimo register as piercing and intense. As the clarinet moves higher and higher within its range, the the lower harmonics become less prominent, which is what causes these subtle timbral variations. Every instrument and voice has similar variations in timbre within different registers.
Other Aspects of Timbre
Attack, the onset of the sound, is another important aspect of timbre. On a string instrument, the sound begins when the bow comes into contact with a string and sets it vibrating. On a reed instrument, the player begins with her tongue touching the reed (preventing it from vibrating), then builds air pressure against the reed, and finally releases the reed so that it can vibrate freely as the air flows through it. These differing techniques cause distinctive patterns of sound at the attack. These patterns are so distinctive that they are critical to our ability to recognize different instruments. When the attack is removed from a sound and we hear only the sustained tone that follows, even trained musicians find it difficult to identify the instrument by ear.
The attack-decay envelope describes how quickly the sound builds to its maximum volume, fades, and ultimately stops. Most instruments do not reach their peak volume instantaneously, but over the course of several milliseconds. The decay of a sound is defined by how long it takes the sound to stop after the original force that caused the vibration has stopped. That is, if you pluck the string of a guitar or press a key on a piano and let it ring, how long does it take the sound to stop? The duration and nature of the attack-decay envelope also contributes to the overall timbre of an instrument.
The purity or impurity of a tone, or the amount and type of noise included in the sound, is another important aspect of timbre. Noise can be caused by breathing or air flow, bow scraping, key clicks, or fingers sliding on strings. These impurities, although often quite subtle, can also help listeners to identify instruments by ear.