You have probably heard of white noise, which is thought of as comforting sounds that help us block out the surrounding environment, like a fan humming away just loud enough that we don’t really hear doors closing or a dog barking outside. In more technical terms, white noise is a random signal that has an equal intensity at different frequencies. White noise is like white light, which contains all visible light at an equal intensity. Fracture that light, and you get a rainbow.
What Is Pink Noise?
Pink noise is a soothing, gentle sound composed of octaves possessing equal energy. In white noise, the power of each frequency is constant, but in pink noise, as frequencies get higher, the difference in power of the associated sounds becomes smaller. The effect is that higher-pitched sounds are softer.This is essentially the nature of background noise we are used to hearing every day. High-pitched sound waves don’t carry as far and are more easily absorbed by whatever they land against, while lower-pitched sounds can penetrate through and carry further. This is why you can hear the bass of a passing car’s stereo more easily than the treble. Pink noise emulates the normal pattern of sounds in our environment.
It turns out, this aspect of pink noise has benefits.
Researchers at Northwestern University in Evanston, Illinois, discovered that if they synced pink noise to the brain waves of older men and women while they slept, the subjects experienced better quality of deep sleep as well as an improvement in memory.
“During sleep, a real-time algorithm using an adaptive phase-locked loop modeled the phase of endogenous slow waves in midline frontopolar electroencephalographic recordings,” wrote the researchers, explaining how they synced the noise to the participants’ brainwaves. The study was published in The Frontiers of Neuroscience in 2017.How Scientists Used Pink Noise
Previous studies in young adults found a link between acoustic (sound) stimulation of deep sleep brain activity and an improvement in memory. These findings prompted Dr. Phyllis Zee, professor of neurology at the Feinberg School of Medicine at Northwestern, and her colleagues to try acoustic stimulation in a group of older adults to see how it affected sleep and memory.The study group consisted of 13 men and women ages 60 to 84 who each were subjected to one night of acoustic stimulation (involving pink noise synced to the participants’ brain waves) and one night of sham (placebo) stimulation. Each of these sessions were conducted one week apart. Before and after each of the sessions, the participants completed two memory recall tests.
- Memory recall was three times better after acoustic stimulation with pink noise than it was with the placebo stimulation.
- The improvement in memory correlated with a boost in the quality of deep sleep and therefore an improvement in sleep quality.