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The Sound of Color

<span  style="font-size: 1.5rem;" >Your first baby is due in two months, and you’re trying to get everything ready. You have a crib, changing table, clothes, and about a million diapers. Then the suggestions start coming in for items you would never have thought of: A nursing pillow? A yoga ball to bounce on? A sound machine? You start to do your research, and pretty soon the internet has convinced you that your baby will never sleep if you don’t invest in a sound machine. Ok, great! Anything you can do to improve the sleep situation. But as you research further, it gets more and more confusing. White noise? Pink noise? Brown noise? How can sound have a color? And what do those colors even mean?</span>

The “color” of sound is really an analogy to the color of light. Vision and hearing work in very different ways in your brain, but many of the tools scientists use to describe light are similar to those for describing sound. Let’s unpack: We’re all familiar with the concept of pitch (the high-pitched squeal of nails on chalkboard versus the low-pitched rumble of thunder). “Pitch” is our everyday word for frequency – the total number of sound waves in one second of time, measured in Hertz (Hz). A high-pitched sound has a high frequency, and a low-pitched sound has a low frequency. You’ll remember Hz if you’ve ever had a hearing test and were told to listen to 500 Hz vs. 1000 Hz sounds. Light can also be described in Hz, with reds being low-frequency and blues being high-frequency.

The visible spectrum.

The color of a sound matches its frequency. Just like colors of light, colors of noise are named for their position on the frequency spectrum. In this sense, sound can be pink in a similar way that light can. And, just like our vision and visible light, sound can exist at levels that are too high or too low for humans to hear. Ultrasound, like ultraviolet light, occurs at a frequency that is too high for the human hearing range, while infrasound, like infrared light, occurs at a frequency that is too low.

While noise can come in many colors, there are three that are most commonly used and discussed. These are white noise, pink noise, and red noise.

As you may know, white light is light that contains all the colors of the spectrum – that is to say, it contains all light frequencies. Similarly, white noise is noise that contains all the sound frequencies we can hear, each frequency at the same strength. This creates what Meghan Neal describes as “20,000 different tones all playing at the same time, mixed together in a constantly changing, unpredictable sonic stew.”1 You can think of white noise as TV static or the sound of your air conditioner. If you don’t find these noises especially pleasant, you’re not alone. One might think that equality across all frequencies would sound the best to the human ear, but although white noise is mathematically elegant, your auditory system isn’t built to hear every frequency equally, so to you it sounds harsh.

Pink noise is actually the noise frequency that sounds more equal (and less grating) to the human ear. This is because it is equal across octaves, which are the doubling of frequencies (so 10 to 20 Hz would be an octave, as would 100 to 200 Hz). Humans don’t hear equally across frequencies, but rather equally across octaves. Pink noise better matches the tuning of human hearing, sounding more like ocean waves or rustling leaves rather than static.

Red noise (also known as brown noise) takes the idea behind pink noise even further. With red/brown noise, the noise frequency is actually less powerful at higher octaves (rather than equal across octaves like pink noise), therefore dampening and reducing the harsher sounding higher frequencies. Red noise sounds more like Niagara Falls or a herd of elephants rumbling across the savannah.2

Votive right ears, bronze, Roman, 200BC-100AD.

Votive offerings were presented in the hope of receiving a cure or as thanks for one to a god. The green color in these ears (the offerings were often made in the shape of the troubled body part) is a result of corrosion from chemical compounds coating the bronze material.

Science Museum Group. Votive right ears. A634920 Science Museum Group Collection Online. Accessed October 28, 2022.

One of the most common applications of white, pink, and red noise is sound machines used for sleep. Although these machines are referred to as white noise machines, they often actually play pink or red noise. So, if you’re on the market for a sound machine or app on your phone, which kind of noise should you look for? This depends both on your personal preferences and on the purpose for which you’re using it.

As we mentioned, a lot of people find white noise downright annoying and irritating. If you are one of these people, a white noise machine may not be for you under any circumstances. However, if you can stand white noise and are in a loud environment, it is very effective at blocking out other sounds. This is because white noise is equally powerful at all frequencies, so it can block out the low rumble of a passing motorcycle just as well as your neighbor’s child practicing the recorder. Low levels of white noise are sometimes used in “noise-canceling” headphones.

Pink and red noise are often said to promote relaxation. The lower, rumbling frequencies have a lulling effect on some people. You may have heard about this noise if you follow TikTok trends. TikTokers have claimed that it’s been a magic solution for everything from sleep to ADHD symptoms.

What about using a sound machine or app to improve work or academic performance? One study2 looked at the usage of red, pink, and white noise in workplace environments. It found that usage of all three types of noise improved performance on a variety of tests of speed, execution, and memory. While there isn’t enough data to know for sure whether and how these kinds of noise improve workplace performance, it could be worth a shot. There isn’t really any downside, and it might just be the boost you need.

Want an easy way to try out pink noise, either to see the effect it has on you or on someone else?

It’s right there in your chest! If you have the opportunity, listen to someone’s heartbeat and notice how you feel, or allow someone to listen to yours and report back on the experience. You can also listen to your own heartbeat with some apps. Compare the sound to other pink noise you hear on a recording or sound machine.

Does it have the same effect?


1 Neal, Meghan. “The Many Colors of Sound.The Atlantic, February 16, 2016.
2 Lu, Shih-Yi et al. “Spectral content (colour) of noise exposure affects work efficiency.” Noise & Health vol. 22,104 (2020): 19-27. doi:10.4103/nah.NAH_61_18.

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