White noise vs brown noise: What’s the best sound for sleeping?

Popular Science...

A friend recently introduced me to Sleep Sounds, an app intended to make sleep easier. With dozens of “audio environments” to choose from, I could drift off to the gentle lapping of waves on a Corsica beach one night and the calls of California wildlife the next. But it was the rumbling of a German express train that left me the most refreshed.  

“Any sounds that you’re perceiving while you’re sleeping definitely affect your sleep,” says Dr. John Saito, a representative for the American Academy of Sleep Medicine. “It’s just like the light that you are experiencing while you are sleeping affects your sleep, and the air that you’re breathing.” 

But which sound—if any—is the most conducive to catching the best zzzzs? Popular Science turned to Dr. Saito to find out. It turns out the answer isn’t so cut and dry. 

How does sound affect our sleep? 

Think of a time when you were sleeping soundly, and suddenly heard a loud bang. All at once, your heart was racing, you were on high alert, and you were no longer tired. Your sleep was disturbed, and in a big way. 

Chronic environmental noise—those background sounds that often come from traffic, airplanes, and passing trains—can also disrupt rest, even if we don’t realize it. 

“Your brain doesn’t switch off like a computer,” says Saito, and continues to process stimuli throughout the night. Such noises can increase stress hormones like cortisol and send your body into fight-or-flight mode, raising your heart rate and blood pressure in the process. 

“Anytime you’re aroused from your sleep state, you’re creating a stressor to your system and your normal pattern of restorative sleep. It perturbs the brain and it causes a change in your physiology,” he says. Physiology is the way in which your body’s parts work together to keep you alive. 

But not all sounds affect all people while they’re sleeping. 

What determines if you’re a deep or light sleeper?

According to Saito, knowing what sounds affect us takes some understanding of sleep architecture, which is the basic structure of our individual sleeping patterns. Sleep architecture maps out how a person transitions through different sleep stages, such as light sleep and dreaming (REM), as well as how sound affects someone during each of these different stages. 

“For people with extremely active brains, any little noise can disrupt their sleeping habits,” says Saito. Then there are those “deep sleepers” whose brains filter out every noise. “There can be a fire alarm ringing and they’ll still sleep like the dead,” says Saito. 

Deep sleepers often produce more “sleep spindles.” These are short bursts of brain activity that help block out external noise. In many cases, the number of sleep spindles a person can generate (and therefore, whether or not someone is a deep sleeper) is inherited. But extreme exhaustion (we’re looking at you, parents!) can also lead to deep sleep. 

What’s the difference between white, brown, and pink noise?

There are many ways that people can perceive the different sounds that they’re experiencing during sleep, says Saito. “It really depends on the individual. So when patients ask me if they should have a white noise machine, I will say ‘what resonates with you best?’ It’s not a particular sound that fits all.”

White noise is a specific type of broadband sound that contains all audio frequencies in equal measure (think of the sound of a ceiling fan or a low “hum”). Many people use it to mask noises that can often be intrusive, such as creaking doors or loud televisions. Still, says Saito, “it can be noise canceling for some individuals and agitating for others. It just depends on the person.” It’s also just one of several “noise colors” that get their names from the way they distribute power across different sound frequencies. Basically, how fast a sound source vibrates. Noise colors can be high-pitched (rapidly vibrating) sounds, low-pitched (slowly vibrating) sounds, or a combination. 

For example, brown noise is a low-frequency, deep-toned sound like thunder or heavy rain, while green noise centers on mid-range frequencies such as ocean waves or a stream. Pink noise is considered balanced and consistent (think of a far-off waterfall) though not as mid-range as green noise. It has more power in its lower frequencies but with less higher frequencies than white noise, which is similar in sound to a fan or a space heater.

So, which is the best noise for sleep—and which is the worst?

Pink noise and other broadband noise colors, which are sounds that contain all audible frequencies (like that static that you hear when switching radio channels) rather than one specific tone, have long been considered good for sleep. But recent studies suggest that they may actually reduce overall REM sleep and harm a person’s sleep quality. Ultimately, “the best sound for sleep depends on your personal preference, as well as your sleep environment and the nature of your sleep problems,” says Saito. 

However, there are some sounds that are especially detrimental to a good night’s sleep. “If you go to sleep with thrash metal music in your ear,” says Saito, “that’s probably not a good idea.” Another no-go? Televisions. “Falling asleep to something playing on the TV is especially bad,” he says, “because not only do you have the sound pollution, but you have the light pollution as well.” 

The thing is, a person might think what they’re doing is restorative. “Their trained behavior might say, ‘I can’t go to sleep unless I have the TV on and playing,’” says Saito. “But even when you’re sleeping, your brain remains active. It’s still receiving and processing both the sound and the light,” negatively impacting the quality of your rest. 

Why the best sleep noise is maybe no sleep noise

Back in the days of early human survival, our hearing helped us detect predators. “We’re kind of tuned to any of these noises that might affect our survival,” says Saito, “any noise, any rustle…really anything that might signal danger.” Preferably, there would be no signs of danger, suggesting maybe the best noise is no noise at all. “That’s generally the ideal,” says Saito, “a sleep environment that’s completely quiet and completely dark.” 

Earplugs, thick rugs, and soundproof curtains can all help to reduce sound rather than add to it, and may all help to improve the quality of your overall snoozing. 

But whether it’s the sound of an air conditioner running or a recording of seabirds chirping that lulls you into a deeper sleep? Well, that really depends on you. In Ask Us Anything, Popular Science answers your most outlandish, mind-burning questions, from the everyday things you’ve always wondered to the bizarre things you never thought to ask. Have something you’ve always wanted to know? Ask us.

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