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When measuring sound waves, “frequency” refers to how fast the waves vibrate per second while “amplitude” (or “power”) refers to the size of the waves. Frequency is measured in hertz and amplitude is usually measured in decibels. The relationship between the frequency and amplitude of a sound wave is used to define different “colors” of noise, which share structural properties with corresponding light waves of the same name.
To produce white noise, every frequency the human ear can hear is played in a random order at the same amplitude. This results in a “shh” sound many associate with television or radio static. Just as white light is thought to be composed of every visible wavelength on the color spectrum, white noise consists of every audible frequency. Fittingly, “black noise” refers to the literal sound of silence.
Disruptive sounds such as a slamming door do not necessarily wake you up because they are loud. Rather, the change in sound consistency from soft to loud can be strong enough to interrupt your sleep. True white noise essentially creates a blanket of sound that masks these sudden consistency changes. And since white noise is audible, it can also be useful for people who do not like sleeping in a completely silent environment.
White noise has proven particularly effective for hospital patients. These settings tend to be quite loud and filled with ambient noise that can disrupt sleep. Studies suggest a white noise machine can reduce sleep onset for patients, or the time it takes to fall asleep, by nearly 40% compared to patients who don’t use these devices. Some studies have also found that white noise can help babies and young children fall asleep more quickly. White noise has also proven effective at helping inattentive children concentrate better in their classrooms.
Some people equate white noise to certain ambient sounds, such as a whirring fan or air conditioner, but they are technically not the same. The effect on your ears may be similar, but by definition, white noise must consist of all audible frequencies played randomly at the same amplitude.
Some sounds confused with white noise are actually different colors of noise. A common example is pink noise. While white noise is defined by equal amplitude across all frequencies, the amplitude of pink noise decreases by half every time the frequency doubles. The result is a blend of more intense low-frequency tones and softer high-frequency tones.
The human ear is particularly sensitive to high frequencies, so many people find pink noise more pleasant than white noise. Pink noise may have other sleep benefits too. Some studies suggest pink noise can actually reduce your brain wave activity. Your brain becomes less active during the initial stages of your sleep cycle. By assisting with this process, pink noise can decrease sleep onset, extend sleep duration, and improve overall sleep quality.
Those who prefer pink noise may also find red noise soothing. Red noise also decreases in intensity as it increases in frequency, but to a more dramatic extent. This produces a low rumbling sound. Alternatively, blue noise increases in intensity as the frequency rises, resulting in more emphasis on high tones and less for low tones. Blue noise can be likened to a fine spray of water.
The best color of noise for sleep will come down to personal preference, If you find high-frequency sounds too harsh, then bass-heavy pink or red noise may be smoother to your ears. If you would rather listen to higher-frequency sounds, white or blue noise might be your best option. We recommend experimenting with different colors using a sound machine that can replicate these noises.
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