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Listening to white noise has been a common strategy for many people hoping to fall asleep more quickly or to stay asleep. Others use it to mask noises when attempting to concentrate while working or studying in a less-than-ideal location, like a noisy coffee shop or the outdoors. But how does white noise work? That is, how does the addition of more noise help us focus, drown out other noises, or even allow us to sleep better?
The short answer? The more noise of white noise keeps us from hearing the unwanted noise.
Just like the color white is made from the combination of all wavelengths of color, so is white noise made from the combination of all wavelengths of sound, which is where the term “white” (and those of the other “colors” of frequency bands) comes from. I.e., if you take all imaginable frequencies audible to the human ear and combine them, you have white noise. Because it contains all frequencies, white noise is often used to mask other noises.
To get at how white (and other color) noise works, first we need to brush up on our fundamentals of acoustics: When measuring sound waves, “frequency” refers to how fast the waves vibrate per second while “amplitude” (or “power”) refers to the size of these waves. The relationship between the frequency and amplitude of a sound wave is used to define different “colors” of noise. The different colors are named such because they share the structural properties of the corresponding light waves of the same name.
White noise isn’t the only “color” of noise that can be generated; other combinations of frequencies produce pink noise and brown/red noise—among others. Each band of frequencies is distinct from the others based on their spectral density. For instance, white noise is called “white” because it has equal energy per cycle, meaning that its frequency spectrum is completely flat.
Pink and brown/red noise, on the other hand, each have different configurations in terms of their frequency bands; pink noise’s frequency spectrum decreases logarithmically over time with equal power bands that are proportionally wide. Its added depth and lower waves filter out higher sounds. As a result, you hear more relaxing, lower-frequency sounds. Brown and red noise are two names for the same thing; its frequency spectrum is heavily weighted toward the lower end of the spectrum, sounding like a low roar. Other “colors” of noise exist, of course; all that’s needed to create these is to manipulate the power of the various frequencies across a spectrum.
As noted earlier, white noise is often used to mask other noises. Why this works is due to the fact that, when layered on top of other noises, white noise will match the frequencies of all other noises around you, making it difficult to distinguish the unwanted noise from the white noise itself. For instance, imagine that you’re in a room, chatting with one person. You can hear their voice clearly; however, if you were to add 100 additional people all talking at the same time, it would be more difficult to distinguish the voice of the person with whom you were trying to have a conversation from any other individual voice without working harder to hear them.
What wakes us from sleep isn’t a loud noise on its own; rather, it’s the change in volume, or sound consistency, that causes some sleepers to slip from slumber. Because white noise creates a masking effect that blocks out other noises/frequencies, such as sudden sounds in the night (e.g., a closing door, a car going by, or a phone falling to the ground in the apartment above you) that jar you from sleep, many people turn to white noise machines as a sleep aid. White noise is similarly used in travel or when studying—times when humans would prefer to avoid the aural distraction of the noises around them.
We’ve always known that quality, consistent sleep over seven hours in length does more for our bodies than simply leaving us feeling rested the next morning. One thing is also for sure, however: Additional research is needed to understand more the benefits (and, some suggest, the risks) of relying on a white noise generator to get to and stay asleep at night.
Interested in playing around with acoustics and learning more about how wavelength, frequency, and amplitude work together to create the sounds we hear? Try using a tuning fork. The fork consists of a handle and two tines. When the tuning fork is hit with a rubber hammer, the tines begin to vibrate. The back-and-forth vibration disturbs the surrounding air molecules, which then reaches your ear as the hum of a pitch.
These particular tuning forks are used for demonstrating the production of beat frequencies, which are created by modifying the frequency of one of the forks using an adjustable mass and sounding both forks at the same time; when both forks are sounded a clearly audible beat is produced, its rate depending upon the difference in frequency between the forks.
The art and science of white noise. (2017, June 14). Pacific Standard. https://psmag.com/news/the-art-and-science-of-white-noise
Geere, D. (2011, July 4). White, pink, blue and violet: The colours of noise. Wired. https://www.wired.co.uk/article/colours-of-noise