A Description of Sound and Its Qualities
The sounds we hear have a great variety, but there are some characteristics common to all sounds that can be used to describe them. Among the most prominent of these are loudness, pitch, and timbre. Although it is helpful in describing and discussing sound to distinguish between these characteristics, it is also important to keep in mind that each of these characteristics can affect the others. For example, when the pitch of a sound changes, its loudness can change as a result.
Loudness
Loudness describes the differences we perceive between the sound of an aircraft heard flying over us at an altitude of several thousand feet and the same aircraft heard taking off at an airport, or between the sound of fireworks several miles away and the sound of fireworks a few hundred feet away, or the sound of traffic from a distant highway and the sound of that traffic while on the highway.
It is a common experience that the sound generated nearby is louder than the same sound generated a distance away. Sound changes with distance in other ways, too, so you may hear other differences between the nearby and distant sounds of traffic. To reduce the complications of the other changes, in the next recording an electronically generated noise changes only in volume, first getting louder, then becoming quieter again.
In an analogy to vision, the loudness of a sound corresponds to the brightness of light. Just as a nearby sound is louder than the same sound at a distance, a nearby lamp is brighter than the same lamp at a distance. Just as a light can be so bright that it hurts to look at it, a sound can be so loud that it is painful. Painfully bright light can damage the eyes, and painfully loud sound can damage the ears.
Pitch
Pitch describes one of the differences we hear between the chirp of a cricket and the call of a bullfrog.
The pitch of the cricket’s chirp is said to be high, while the pitch of the bullfrog’s call is low. There is a difference in pitch between the sound of a coin dropped on a hard floor and the sound of a metal pan dropped on the same floor.
The ring of the dropped coin is higher in pitch than the clang of the fallen pan. –
With these natural sounds, there are other differences in addition to pitch. To isolate pitch from the other effects, the next recording is electronically generated so that only the pitch changes, changing gradually and continuously from a lower pitch to a higher pitch. [1]
Some sounds have a very definite and precise pitch. Other sounds have a more indistinct pitch. The sound in the next recording alternates between two quite distinct pitches.
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The sounds that alternate in this recording have distinct pitches. Sounds with a distinct pitch are called pure tones. The sound in the next recording also alternates between pitches, but the pitches are indistinct.
The sounds that alternate in this recording are not pure tones. In fact, the word that is used to describe sounds that do not have a distinct pitch is noise.
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In analogy to vision, the pitch of a sound would correspond to the color of light. The color of light can vary continuously over a spectrum from red through orange and yellow and green and blue to violet. The pitch of a sound can vary continuously, too, from a low pitch to a high pitch. Some colors appear very pure, such as those produced by a prism in sunlight, or the light from a laser pointer. Other colors appear indistinct or dim, such as a wilted flower or the mud in a puddle. Similarly, some sounds have a pitch that is clear and pure, while others have a pitch that is indistinct and unclear. We will see later that there is more to this similarity between pitch and color than a mere analogy.
Timbre
Timbre (pronounced TAM-ber) refers to the difference between sounds that have the same pitch and loudness, but still sound distinct. In the following recording seven different musical instruments play the same pitch (the standard “A 440”) in sequence. The instruments are: oboe, harp, French horn, tubular bell, clarinet, piano, and flute.
The sounds all have the same pitch, yet they are all different. The difference between them is in the timbre of each instrument. Each has its own particular timbre, and it is the timbre that makes each recognizable as the instrument it is. No musical instrument produces a pure tone. Each produces a combination of tones that is particular to that instrument, a combination that gives it its recognizable sound. Even though each instrument produces a combination of tones, we hear only a dominant one, the one that gives a specific pitch to the combination of tones.
[1] Different sound reproducing equipment, such as headphones versus computer speakers versus high-fidelity speakers, responds differently to an input signal. Therefore, it is possible that the system you are using to listen to the pitch sweep may change in loudness as well as pitch. However, such a loudness change should not be great enough to interfere with your experience of pitch.