Commercially available white noise generators are a popular option for people who have trouble sleeping. Clinical and anecdotal evidence suggests the technology works. But how does it work?
In this DNews report, Amy Shira Teitel explains how color is a useful metaphor for understanding white noise. Just as white light includes all colors, white noise incorporates all the frequencies of the sound "spectrum" that we can pick up with our ears.
If it's playing loud enough, white noise essentially masks other sounds by drowning them out. Human auditory range spans 20 hertz to 20,000 hertz, more or less, with hertz being a metric for measuring repeating vibrations per second.
At night, that sound that wakes you up is typically a spike -- a sudden change in frequency relative to background noise. Even while you're asleep, your ears are registering significant sounds in the environment and translating them into electrical impulses that are piped into the brain.
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White noise generators work by flooding the brain with "flat" ambient sound at all frequencies. Again, the color metaphor is helpful: Just as white light is all wavelengths of light, white noise is all frequencies of sound. Any noise spike that could potentially disrupt your sleep is lost in the aural blanket of frequencies.
Interestingly, recent studies suggest that a different shade of sound, as it were, may be even more effective than white noise. Pink noise also contains all frequencies audible to the human ear, but whereas white noise has equal power per hertz at all frequencies, pink noise decreases in power as frequency increases.
In other words, with pink noise the lower bass frequencies are louder. This pattern occurs in natural systems as well, including your daily heartbeat rhythms and even quasar luminosity.
You can check out the video above to hear some audio samples of both white noise and pink noise. There are other noise colors, too -- blue, violet, green, orange and even black. Who knew?
White noise generators don't work for everyone, but they definitely help a good percentage of people who have trouble with waking up during the night. And whatever the color, the technology's basic function is to mask those other noises that nudge the brain during sleep.
-- by Glenn McDonald Read More:
PopSci: Why Does White Noise Help People Sleep?
Wired: White, Pink, Blue and Violet: The Colours of Noise
Live Science: What Is Pink Noise?