Brightness / Darkness
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Brightness / Darkness
by Jason Noble
Timbre Lingo | Timbre and Orchestration Writings
“Brightness” is one of the most common terms used to describe sounds, drawing on strong cross-modal associations. Most people can call to mind examples of “bright” sounds: what do these sounds have in common?
Most sounds are made up of multiple different sound components, including partials and noise components. The relations between sound components have a big impact on how the overall sound is perceived: for example, simple numerical ratios between frequencies of partials produce tightly fused sounds with clear pitch, while complex ratios produce more diffuse sound images with a weaker sense of pitch (see previous Timbre Lingo post on Inharmonicity).
Another important factor in the perception of complex sounds is the distribution of energy: where in the frequency spectrum is a sound’s energy concentrated? Two sounds might have the same fundamental frequency, the same number of partials, and the same numerical ratios between those partials, but still be perceived as different because of differing distributions of energy between the partials (which would likely correspond with differing spectral centroids). Distribution of energy is closely linked to the sensation of the sound’s brightness or darkness. Sounds with a lot of energy in higher partials tend to be perceived as brighter, while sounds with most of their energy in lower partials tend to be perceived as darker. For example, if pitch and loudness are equal and standard playing techniques are used, trumpets are perceived as brighter than horns, oboes are perceived as brighter than flutes, and harpsichords are perceived as brighter than pianos, because of differing distributions of energy between these pairs of instruments. The same holds true for noise-based sounds that lack clearly defined partials: a sound with noise components in the high register, such as a triangle, will be perceived as brighter than a sound with noise components in the low register, such as a large woodblock.
It should be noted that musicians sometimes differ in how they use these terms: for example, the opposite of “bright” is not always “dark.” For example, some would use “dull” instead of “dark” as the opposite of “bright.” For many flutists, a “dark” sound is a concentrated sound with lots of harmonic content, as opposed to a "whiter" sound, which has more noise content. It should also be noted that there may be other factors relevant to the perception of brightness, such as loudness, reverberation, and knowledge of the sound source. Nevertheless, brightness is one of the few semantic associations with sound for which a clear correlation with an acoustical feature is well-understood.
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