What is white noise?

The term “white” is used to characterise this form of noise because of the way white light functions. White light is light that is made up of all of the many colours (frequencies) of light united together (a prism or a rainbow splits white light back into its component colours) (a prism or a rainbow separates white light back into its component colors). In the same manner, white noise is a collection of all of the distinct frequencies of sound. You may think of white noise as 20,000 tones all playing at the same time.

Because white noise encompasses all frequencies, it is commonly employed to hide other noises. If you are at a hotel and sounds from the room next-door are seeping into your room, you could switch on a fan to drown out the noises. The fan creates a reasonable imitation of white noise. Why does it work? Why does white noise block out voices?

Here is one way to think about it. Let’s assume two persons are chatting at the same moment. Your brain can generally “select out” one of the two voices and truly listen to it and comprehend it. If three individuals are talking simultaneously, your brain can probably still pick out one voice. However, if 1,000 individuals are talking simultaneously, there is no way that your brain can choose out one voice. It turns out that 1,000 individuals conversing together sounds a lot like white noise. When you turn on a fan to generate white noise, for example, you are effectively producing a source of one thousand separate voices. The voice next door brings the total number of voices to 1,001, and at this point, your brain is unable to distinguish between them.

White Noise
Color-coding sound

When I was growing up, the window in my bedroom was outfitted with an air conditioning unit so that it could be used during the summer months. Even though it helped to keep the space cooler, the warm summer evenings I spent turning it on were some of my favourites. The sound, which I found to be incredibly calming, was the aspect that I like the most. Years later, when I was enrolled in college, I had a friend who was the subject of widespread ridicule due to the fact that he was unable to fall asleep unless he had a radio playing static next to his bed. The sound of static on a radio, for some reason, felt funny in a way that the sound of an air conditioner did not, yet they amounted to basically the same thing: white noise, which has a well-known capacity to encourage sleep by masking other noises. In this case, the sound of an air conditioner.

The vast majority of us have come across white noise generators or CDs that include white noise that are marketed as sleep aids; in certain cases, these products are marketed specifically for newborns. When testing and calibrating professional audio equipment, a specific kind of white noise generator is employed. However, what precisely is white noise, how exactly does it function, and why is it referred to as “white” noise?

Pure Noise

White light is a mixture of all the other colours of light; by using a prism, we can divide it into its component hues. If you look back to your primary school science studies, you undoubtedly learnt that white light is a combination of all the other colours of light. According to the comparison, “white” noise is made up of noises of all frequencies that fall within the range of human hearing, which is around 20 to 20,000 Hz (cycles per second), with each region of the frequency spectrum having an equal amount of loudness (volume). Because of its unpredictable and chaotic character, it is referred to as “noise” rather than “sound.” Instead of simply producing a tone at 20 Hz, 21 Hz, 22 Hz, and so on all the way up to 20,000 Hz, a white noise generator creates a constantly changing mixture of tones such that all frequencies have an equal probability of being audible at any given moment. This ensures that the sound is not distinguishable based on the frequency of the tone.

A hissing sound is what white noise sounds like to human hearing; other noises that are quite comparable to white noise are those of a waterfall, an aerosol can, and static. White noise contains all frequencies, but we hear it as having a relatively high pitch. This is due in part to the fact that higher octaves contain a wider range of frequencies than lower ones, which gives the higher-frequency sounds proportionally more energy, and in part to the fact that our ears are more sensitive to higher-pitched sounds.

Because it efficiently overwhelms or “numbs” our auditory systems, white noise is adept at masking most other types of sound, making it an effective sound masking tool. When you’re already hearing sound at every frequency, it’s difficult for your brain to distinguish any one sound or voice because there are so many competing ones. This is similar to how it might be challenging to carry on a conversation at a busy restaurant. Consequently, it is not the white noise itself that induces sleep as much as the fact that it minimises the amount of aural clutter by drowning out other noises that may distract you and therefore keep you awake. This is the primary mechanism by which white noise works.

The Color of Sound

If there is sound present at every frequency in “white” noise, then you may think it would be feasible to generate additional “colours” of noise by giving more weight to particular frequency ranges than others. And you’d be absolutely correct. There is such a thing as pink noise, in addition to red, orange, green, blue, purple, grey, brown, and even black noise. Pink noise is only one of the many types of noise that exist. Out of them, pink noise is the most prevalent and can be classified in the most straightforward manner. In contrast to white noise, which has the same amount of energy at every frequency, pink noise has the same amount of energy within each octave. To put it another way, the amplitude at higher frequencies is decreased so that it may be perceived by the human ear as having a more balanced tone. One of the many applications for pink noise is in the calibration of speaker systems. When we refer to anything as “pink,” we mean that it is similar to white, but it is “tinted” or skewed toward the sounds that have lower frequencies (and, as a result, longer wavelengths). In any event, the colour labels are nothing more than a handy metaphor to represent white noise that has been filtered in different ways. However, not all of the so-called noise colours translate onto the visible spectrum in such an obvious manner.

Many of the devices on the market that claim to be able to make white noise are really recordings or simulations of noises like wind, waves, and other phenomena that are, in fact, far more complicated than white noise. It’s not that there’s anything wrong with it—the sound of rain on the roof may be extremely relaxing, and it can have much of the same advantages as white noise in terms of obscuring other sounds. And in the same way that the definition of the phrase “white noise” may be broadened to encompass what you could call “off-white” noise, it can also have a more metaphorical connotation, such as in “meaningless chatter.” But what I really want to hear is a tape that recreates the sound of my previous air conditioner, replete with the hum that the compressor generated whenever it kicked on. That would be more effective than taking a melatonin pill followed by a warm glass of milk, in my opinion. —Joe Kissell

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