Pink noise and brown noise are two types of sound signals defined by how their energy is distributed across frequencies. Pink noise emphasizes lower frequencies more than higher ones, dropping off at about 3 decibels per octave. Brown noise takes that emphasis further, concentrating even more energy in the bass range with a steeper drop of about 6 decibels per octave. Both sound deeper and softer than white noise (which treats all frequencies equally), and both have become popular tools for sleep, focus, and relaxation.
How Pink Noise Works
Pink noise follows what physicists call a “1/f” pattern: as the frequency doubles, the power cuts in half. In practical terms, this means it still contains high-pitched sounds, but they’re quieter relative to the low-pitched ones. The result is a full, balanced sound that most people describe as warm and even. Think of steady rain on a roof, wind blowing through trees, or a rushing river. These natural sounds tend to follow a similar frequency pattern, which is one reason pink noise feels familiar and pleasant rather than harsh.
Because of its balanced spectrum, pink noise has drawn attention in audiology. A 2023 study published in the American Journal of Translational Research found that pink noise was more effective than white noise for relieving tinnitus symptoms. The researchers noted that pink noise’s energy is concentrated in the mid-to-low frequency range, which matches the pitch of many common forms of tinnitus better than the flat, hissing quality of white noise. Its waveform also has a fractal structure, meaning it repeats similar patterns at different scales, giving it a natural, non-irritating quality even over long listening sessions.
How Brown Noise Works
Brown noise (sometimes called Brownian noise or red noise) is named after Robert Brown, the botanist who first described the random motion of particles suspended in fluid. The signal mimics that kind of random, drifting movement, and the sound reflects it: deep, rumbling, and heavy. Its power drops at 6 decibels per octave, twice the rate of pink noise, so the higher frequencies are much quieter by comparison. What you hear is dominated by bass.
If you’ve ever stood near a large waterfall, listened to thunder rolling in the distance, or heard the low drone inside a moving car, you’ve heard something close to brown noise. It lacks the mid-range and high-frequency content that gives pink noise its fuller character. For many listeners, that deep, enveloping quality is exactly the appeal. Brown noise has become especially popular online among people with ADHD who say it helps them concentrate, and there’s a plausible neurological reason for that.
Why People Use Them for Focus
A key concept behind both pink and brown noise is stochastic resonance, a phenomenon where a moderate amount of background noise actually improves signal detection in the brain. Research from Stockholm University found that people with ADHD performed better on cognitive tasks when exposed to noise, while neurotypical participants showed no benefit or slight declines. The explanation centers on dopamine: individuals with lower baseline dopamine activity (common in ADHD) need more external stimulation to reach their optimal level of neural arousal. Background noise provides that stimulation without being distracting the way speech or music can be.
The original study used white noise, but many people with ADHD report preferring brown noise specifically because its deeper tone feels less grating during extended use. Pink noise sits in the middle and works well for people who want a fuller soundscape without the hiss of white noise or the heaviness of brown.
Pink Noise and Sleep
Pink noise has received the most research attention as a sleep aid. The leading hypothesis, outlined in a 2025 review in PMC, suggests that pink noise reaches deep brain structures involved in memory processing. Specifically, researchers propose that the sound may increase the likelihood of sharp-wave ripples in the hippocampus, brief bursts of neural activity that help transfer memories from short-term to long-term storage. When these ripples synchronize with the slower brain waves of deep sleep, memory consolidation improves.
That said, the picture isn’t entirely straightforward. A 2023 study in Frontiers in Human Neuroscience tested 72 participants and found that playing pink noise continuously throughout the night (open-loop, meaning it wasn’t timed to brain wave cycles) did not increase the amount of deep sleep compared to sleeping in silence. More surprisingly, the pink noise group showed reduced insight formation on a pattern-detection task the next morning, performing more like the group that had stayed awake. The researchers suggested that untimed pink noise may subtly disrupt normal sleep architecture even when total sleep time stays the same.
The takeaway: pink noise timed to specific phases of deep sleep (closed-loop stimulation, typically done in lab settings) appears to have real benefits for memory. Playing it on a loop all night from a phone or speaker is a different thing entirely, and the evidence for that approach is weaker and more mixed.
Brown Noise and Sleep
Brown noise hasn’t been studied as directly for sleep as pink noise has, but its deep frequency profile makes it effective at masking low-pitched environmental sounds, the kind most likely to wake you up. Truck engines, HVAC systems, neighborhood bass, and snoring all sit in the low-frequency range where brown noise has the most energy. If your sleep disruptions come from those kinds of sounds, brown noise may be more effective than pink or white noise simply because it covers that part of the spectrum more thoroughly.
How They Compare to White Noise
- White noise has equal energy at every frequency. It sounds like TV static or a hissing fan. Some people find it harsh, especially at higher volumes.
- Pink noise rolls off the high frequencies gently (3 dB per octave). It sounds like steady rain or a river. Most listeners perceive it as more natural and balanced than white noise.
- Brown noise rolls off the highs more aggressively (6 dB per octave). It sounds like a low rumble, heavy rain, or distant thunder. It’s the deepest and most bass-heavy of the three.
The color naming system follows a loose analogy to light. White light contains all visible wavelengths equally. Pink light is red-shifted (lower frequency). Brown (or red) shifts even further toward the lowest frequencies. The terminology can be inconsistent in casual use, but the decibel-per-octave slopes are the precise way to distinguish them.
Listening Safely
Because many people play these sounds for hours, especially overnight, volume matters. The CDC notes that sounds at or below 60 decibels (roughly the level of normal conversation) are safe for any duration. Sounds at 85 decibels and above can cause noise-induced hearing loss with repeated exposure over months or years. Most sleep sound machines and phone apps let you set a specific volume level. A good rule of thumb: if you need to raise your voice to talk over the noise, it’s too loud. For overnight use, keeping the volume just loud enough to mask disruptive sounds is both safer and more effective than cranking it up.
Earbuds and headphones deserve extra caution. They deliver sound directly to the ear canal, and what feels like a moderate volume can actually be higher in decibels than the same sound played through a speaker across the room. If you use earbuds overnight, setting them to a low, comfortable level before you fall asleep is important since you won’t be able to adjust once you’re out.