Pink noise for sleep
Q: I’ve heard that “pink noise” is more effective than white noise for sleep. Is that true?
A: They both may help, but it’s not clear whether one type is more effective than the other since no studies have compared them head-to-head. The various “colors” ascribed to noise—in addition to white, there are also pink, blue, and brown noise—refer to differences in the distribution of the frequencies audible to the human ear that make up the noise. The colors of noise may be thought of as analogous to the colors of light. Just as white light is made up of all the colors of the rainbow that humans can see, white noise is made up of all the sound frequencies that humans can hear, with every frequency distributed equally.
Examples of white noise include the sound of steam hissing from the radiator or static on the television. There’s considerable evidence that white noise is effective for promoting sleep. It creates a constant ambient sound that helps to mask other noises, like a car door slamming outside, which might wake the person up.
Pink noise is like white noise, but instead of having equal power across frequencies, pink noise comes out louder and more powerful at the lower frequencies. Pink noise is often found in nature, such as waves lapping on the beach, leaves rustling in the trees, or a steady rainfall. Brown noise is even more skewed toward the lower frequencies, so the sound is deep, like the sound of thunder or the low roaring of a waterfall. Brown noise may sound less harsh than white or pink noise. With blue noise, higher frequencies are emphasized, such as a high-pitched hissing of water. There’s more research on pink noise than on brown or blue noise, but far less than on white noise.
Research on pink noise
In a small study in 2012 in the Journal of Theoretical Biology, Chinese researchers tested the effect of pink noise on adult participants during nighttime sleep and daytime napping. The subjects’ brain activity was measured while they slept. The investigators noted an improvement in deep sleep—the more refreshing, restful stage of sleep—at night, and an even larger improvement during daytime napping, when the subjects listened to pink noise compared with no noise. The participants also reported sleeping better on average in the pink noise condition.
In another study, published in Neuron in 2013, researchers synched pink noise with participants’ brain waves, so that it played when their brain activity registered deep sleep. Compared with no noise, the pink noise corresponded with a longer duration of deep sleep. Interestingly, the subjects were also able to recall almost twice as many word pairs shown to them the previous night after sleeping with pink noise, vs. no noise. Two newer studies, published in 2017 in Frontiers in Human Neuroscience and 2016 in Sleep Medicine, respectively, also found benefits of pink noise on deep sleep and memory. But more research is needed to determine whether these benefits would translate to real-world sleep situations, as well as how pink noise compares to white noise or other noise colors.
Bottom line: If you want to try listening to one of the colors of noise to help you sleep, you may need to experiment with the type of noise and volume, since not everyone responds the same way. There are smartphone apps—such as Noisli or Simply Noise—that offer a variety of pink noise as well as white and brown noise. Or you can stream pink and other noises online from various websites, including playnoise.com.