Brown noise is a random sound whose power falls steeply with frequency, in proportion to 1/f²: minus 6 decibels per octave, twice as steep as pink noise. Most of its energy sits in the low range, so it sounds like a deep, steady rumble, with almost none of the hiss of white noise. The name comes from Brownian motion, not from the color. Research on brown noise itself is very thin: we found no controlled study of brown noise for sleep or focus in adults. What can be said comes from studies of steady noise in general, and from one 2025 study that found white, pink and brown noise affect arousal the same way.
This page goes deeper on brown noise alone. For how it compares with white and pink noise, see our guide to white, pink and brown noise.
Brown noise, physically
The spectrum. Brown noise has power proportional to 1/f². Double the frequency and the power per hertz drops to a quarter. That's minus 6 dB per octave, or minus 20 dB per decade. An engineering textbook chapter on noise (Woolf, Engineering LibreTexts) puts it simply: brown noise "has more energy at lower frequencies" and is "even more soft and damped" than white or pink noise.
The name. The same source explains that brown noise is "created by Brownian, or random, motion" and "can be compared to a random walk." The Sleep Foundation notes that it's also called red noise.
The random walk. That's the most useful way to picture it. White noise is a new random value at every instant, unrelated to the last. Brown noise is the running total: each value is the previous one plus a small random step. That's why the textbook says brown noise "can be generated by integrating white noise." Because each value leans on the one before, the signal moves in slow swells rather than jumping around, which is what you hear as a rumble.
Where it shows up. The textbook notes that interference in instrument readings from sources like nearby machinery vibrations often has a brown noise pattern, and that liquid moving in a pipe tends to produce brown noise.
Brown noise frequency: why it can drift, and what the app does about it
A pure random walk has a problem: it can wander off without limit, because nothing pulls it back. For audio, that would mean more and more power at ever lower frequencies, far below anything you can hear, until the signal clips.
The app solves this the usual way, with a leaky integrator (from the app's code): at every step, the running total is shrunk very slightly before the next random step is added, by a factor of 1/1.02. That small leak pulls the signal back toward zero. The effect on the spectrum: above a certain corner frequency, the sound falls at the brown-noise slope of minus 6 dB per octave; below it, the curve levels off.
Our calculation of that corner, from the code's values, is derived, not measured:
- Formula: corner frequency ≈ sample rate × ln(1.02) ÷ (2π)
- Inputs: sample rate 44,100 Hz (app code), leak factor 1.02 (app code)
- Result: about 139 Hz
So the app's brown noise is brown from roughly 139 Hz upward and flat below it. That keeps the rumble steady instead of drifting, while the part of the sound that makes it "brown", the steep drop into the treble, stays in place. What you actually hear also depends on your speaker: we have not measured the output of a phone.
What brown noise sounds like, in the app and elsewhere
AI Meditation: Sleep & Calm describes its brown noise as "a deep, low rumble like distant surf or heavy rain. Warm and grounding for focus and relaxation." The Sleep Foundation compares brown noise to rainfall or a shower. Both are comparisons, not recordings: the app has no nature recordings. It generates brown noise live on your phone, so there's no loop point.
You can set a timer from 5 to 90 minutes, after which it fades out and stops, or let it play until you stop it.
What research says about brown noise
Very little, and we looked. On September 25, 2026 we searched PubMed for "brown noise", "Brownian noise" or "red noise" in titles and abstracts together with sleep, relaxation, attention or listening. The search returned 22 records. None was a controlled trial of brown noise for sleep or concentration in adults; most were from other fields, such as physics, signal analysis or perception research. The Sleep Foundation reaches a similar verdict: brown noise's "effect on sleep has not been widely studied." Two records are relevant:
- Arousal is the same across colors. In a 2025 study from University College London, 38 people were recruited and 31 analyzed. They listened to white, pink and brown noise for 10 seconds each while their pupil size, a marker of how alert the nervous system is, was recorded. There was no significant difference between the three. The authors write that "despite widespread claims about the distinct arousing or calming properties of coloured noises, they do not differentially affect sustained pupil-linked arousal in naïve listeners." It's a short, lab-only test, not a sleep study, but it's the closest thing to a direct test of the "brown noise calms you" idea.
- One hospital study used it, but can't isolate it. In a 2022 study in a hospital high dependency unit in India, 54 patients used a noise app twice a day for three days: white noise on day 1, pink on day 2, brown on day 3, through noise-isolating earphones. Sleep quality ratings improved compared with a control group on all three days. Because the order was fixed and earphones also block sound, the study can't show what brown noise did on its own.
So "brown noise helps you sleep" and "brown noise helps you focus" are, as of today, claims without direct evidence. That doesn't mean it doesn't help you; it means nobody has shown it.
Brown noise for sleep: what can be said
Since there's no brown-noise sleep study, the best guide is research on steady broadband noise in general, which our comparison guide covers in detail:
- A 2021 systematic review of 38 studies rated the evidence that continuous noise improves sleep as very low quality, and warned it may also affect sleep and hearing.
- A 2026 sleep lab study found that pink noise all night reduced REM sleep, and that earplugs protected sleep from environmental noise better. Brown noise wasn't tested, but it is broadband noise too, and the authors called for more research on the best color and level.
What that means in practice: brown noise is a reasonable choice if you need to cover something and find hiss annoying. Keep it low and let it fade out once you're asleep.
Brown noise vs white noise, and brown vs pink
- Brown vs white: white noise has equal power at every frequency and sounds like a bright hiss; brown noise puts most of its power in the bass. The 2025 pupil study found no difference in arousal between them. See white noise.
- Brown vs pink: both lose power toward the treble, brown twice as fast. Pink still has a soft hiss; brown is mostly rumble. See pink noise.
- Brown vs white for sleep: no study compares them head to head for sleep in adults. If white noise sounds sharp to you, brown is the gentler test.
Brown noise for studying
Brown noise is a popular focus sound, but we found no controlled study on brown noise and concentration in adults. The one controlled office study we checked, from 2022 with 39 graduate students, used white noise: at 45 dB it went with better attention and lower stress than normal office sound, while 65 dB raised stress. Our comparison guide describes it. If you study with brown noise, keep it low and check honestly whether you get more done.
How to use brown noise, and how loud is safe
- Start quiet and turn it up only until the sound you want to cover fades into the background.
- Use a speaker, not earbuds, and keep the phone away from your head.
- Set a timer that fades out after you fall asleep.
- Try earplugs if the noise you're masking is loud. In the 2026 lab study, they worked better than noise.
- Mind your hearing. The US National Institute on Deafness and Other Communication Disorders (NIDCD) says sounds at or below 70 dBA are unlikely to cause hearing loss even after long exposure, while long or repeated exposure at or above 85 dBA can. The WHO suggests keeping your device's volume at no more than 60% of maximum. The sleep studies in our comparison guide used about 40 to 50 dB; the WHO puts a library at about 40 dB and normal conversation at about 60 dB.
Brown noise in the app
AI Meditation: Sleep & Calm has brown noise alongside white, pink, blue, violet and grey noise, and four soft tonal sounds: Deep tone, Warmth, Crystal and Resonance, a singing bowl tone. If you'd rather fall asleep to a voice, there are guided sleep meditations and sleep stories, read by AI voices. For the rest of your evening, see our sleep hygiene checklist. See how the app works, try it for free, no account needed.
Your health
This app is a wellness app and does not replace medical advice. If sleep problems last for weeks or affect your day, talk to a doctor. If you notice changes in your hearing, see a doctor as well. The NHS insomnia page explains when to see a GP about sleep.
Sources
All pages accessed on September 25, 2026.
- Woolf P. et al.: Noise Modeling: White, Pink, and Brown Noise, Pops and Crackles, in Chemical Process Dynamics and Controls, Engineering LibreTexts (CC BY 3.0). Brownian motion, random walk, integrating white noise, examples.
- Sleep Foundation: White Noise: What It Is and How It Can Help You Sleep (updated July 29, 2025). Red noise, twice the drop of pink noise, rainfall and shower comparison, little sleep research.
- Erfanian M, Chait M, Kang J: Pupil-linked arousal does not differ between 'white', 'pink' and 'brown' noises. International Journal of Psychophysiology 2025;218:113271.
- Warjri E et al.: Impact of a white noise app on sleep quality among critically ill patients. Nursing in Critical Care 2022;27(6):815-823.
- PubMed search, run by us on September 25, 2026: "brown noise", "brownian noise" or "red noise" in title or abstract, combined with sleep, relaxation, attention or listening (22 records).
- Riedy SM, Smith MG, Rocha S, Basner M: Noise as a sleep aid: A systematic review. Sleep Medicine Reviews 2021;55:101385.
- Basner M et al.: Efficacy of pink noise and earplugs for mitigating the effects of intermittent environmental noise exposure on sleep. Sleep 2026;49(5):zsag001.
- Awada M et al.: Cognitive performance, creativity and stress levels of neurotypical young adults under different white noise levels. Scientific Reports 2022;12:14566.
- NIDCD: Noise-Induced Hearing Loss (last updated April 16, 2025). 70 and 85 dBA.
- WHO: Deafness and hearing loss: Safe listening (questions and answers, March 6, 2026). 60% volume, decibel examples.
