Brown Noise

A deep, low-frequency rumble — closer to a waterfall heard through a wall than to static. Measured on this player at −5.98 dB per octave.

What Brown Noise Actually Sounds Like

Brown noise is the darkest of the common noise colours, and most people reach for water to describe it: a strong waterfall, a river in flood, surf heard from the top of a cliff. Others hear machinery instead — the cabin drone of a long-haul flight at cruise, a tumble dryer two rooms away, wind pushing steadily against a window at night. What every one of those has in common is that the detail sits low. There is body and weight to the sound, and almost no hiss on top of it.

Put side by side with white noise the difference is not subtle. White noise sounds like it is arriving from a point somewhere in front of you — bright, papery, a little abrasive. Brown noise sounds like it is coming from the room itself. That enveloping quality is why it is the colour people most often pick for a full night rather than a twenty-minute session, and why listeners who bounced off white noise years ago tend to get on with it immediately.

The player above generates brown noise continuously rather than looping a recording, so there is no repeat point at all. Nothing to notice at three in the morning, nothing to start listening for once you have heard it a few hundred times.

The Spectrum, Measured Rather Than Quoted

Brown noise — also called Brownian noise or red noise — has a power spectral density that falls by 6 decibels for every doubling of frequency. Halve the frequency and the power quadruples. That is the textbook definition, and nearly every page written about brown noise repeats it. Very few of them have checked whether the sound they are serving actually does it.

This one was measured. Over 120 seconds of output at 48 kHz, analysed with Welch's method and fitted by least squares between 100 Hz and 10 kHz, the slope came out at −5.98 dB per octave, deviating from a straight line by no more than ±0.36 dB across that whole range. That is the −6 dB per octave ideal, within a third of a decibel.

In practical terms it means the energy is stacked hard at the bottom. By 1 kHz — roughly the region where the vowels of ordinary speech live — brown noise has already shed about 20 dB relative to 100 Hz. Above about 5 kHz there is very little left at all. That single fact explains almost everything brown noise is good at, and everything it is bad at.

One more measurement worth stating, because it affects how the site feels rather than how it looks on paper: all five colours here are normalised to −20 LUFS using ITU-R BS.1770-4 K-weighting, with only 0.6 dB of spread between them. Equal-energy noise is not equal-loudness noise, so without that step brown would sound almost inaudible next to blue. The left and right channels are also generated from independent random sequences (measured correlation around 0.005), so the stereo image is genuinely wide rather than one mono signal copied to both ears.

What Brown Noise Is Genuinely Good At

Low-frequency intrusions. Traffic rumble, an HVAC unit, a lift motor, the bass from a neighbour's music, footsteps on the floor above. Auditory masking works best when the masker and the unwanted sound occupy the same part of the spectrum, so a low-frequency problem needs a low-frequency masker. Brown noise is the only colour on this site with real power below 100 Hz, and for these specific complaints nothing else here comes close.

Long sessions. The absence of high-frequency energy is the reason people can leave brown noise running for eight hours without the sound starting to grate. Listening fatigue from broadband noise is largely a treble phenomenon; brown noise simply has no treble to fatigue you with.

Listeners who dislike white noise. If you have tried a white noise machine and described it as sharp, tinny, or like a hiss inside your head, brown noise is the obvious next thing to try. It is the same idea executed at the opposite end of the spectrum.

Layering. Because it sits so low, brown noise stacks underneath rain, music or a fan without fighting them for the same frequency range. In the Android app this is what sound mixing is for — brown noise as a floor, with rain or thunder on top of it.

What Brown Noise Is Bad At

It cannot mask anything high. A smoke-alarm low-battery chirp, a phone notification, birdsong at first light, the sibilance of speech leaking through a wall — all of these sit in a region where brown noise has essentially nothing left to offer. If the thing keeping you awake is a conversation rather than a lorry, white or green noise will do more for you than brown will, no matter how loud you set it.

It needs hardware that can reproduce it. Phone speakers, laptop speakers and small Bluetooth pucks roll off steeply below roughly 200–300 Hz, which is exactly where most of brown noise's energy lives. Played through them, brown noise is not merely quiet — a large part of it is missing. The instinctive response is to turn the volume up, which only raises the fraction the speaker can actually produce. Headphones or a speaker with a real driver change the experience so completely that it is worth testing before deciding brown noise is not for you.

It travels. Low frequencies pass through walls, floors and doors far more readily than high frequencies do — the reason you hear a neighbour's bass line and not their dialogue. If you live in a flat or share a wall with a light sleeper, brown noise is the colour most likely to become somebody else's problem.

Sustained low-frequency sound does not suit everyone. Some listeners describe a sensation of pressure or fullness in the ears after a while. If that is your experience, pink noise gives you a similar unhurried character with a good deal less weight at the bottom, and green noise removes the sub-bass region entirely.

What the Research Does and Does Not Show

The honest position on brown noise is that there is almost no research on it specifically, and pages that imply otherwise are overselling.

The most relevant systematic review is Riedy and colleagues, Noise as a sleep aid: A systematic review (Sleep Medicine Reviews, 2021), which examined continuous white noise and similar broadband noise as a sleep aid across 38 articles. Its conclusion was not the ringing endorsement it is often quoted as: the evidence that continuous noise improves sleep was judged to be of very low quality, and some of the included studies reported no benefit or worse sleep. Nothing in that review isolated brown noise as a condition.

The other frequently cited work is about different colours and different outcomes altogether. Nigg and colleagues (Journal of the American Academy of Child and Adolescent Psychiatry, 2024) pooled the trials on white or pink noise and laboratory attention tasks, and found a small benefit for people with ADHD or high ADHD symptoms — and no benefit for anyone else. Once again, brown noise was not the sound under test.

What is uncontroversial is the acoustics. Auditory masking is settled physics: a sound raises the threshold at which you can detect other sounds close to it in frequency, and a −6 dB per octave signal is unusually well suited to masking low-frequency household noise. Whether reliably masking noise translates into measurably better sleep is a different question, and it has not been answered well for any colour — and has barely been asked for this one.

So: if brown noise works for you, use it. It costs nothing, it is not a drug, and at a sensible volume it has no obvious downside. Just treat any page that describes it as clinically proven — including any app store listing — with scepticism. Nothing here is medical advice, and a sleep problem that persists is a conversation to have with a clinician rather than with a noise generator.

Getting the Most Out of It

Set the volume by the intrusion, not by the noise. Turn it up only until the sound you are trying to cover stops being distinct, then stop. Past that point extra volume buys you no extra masking — the intrusion is already gone — and simply adds exposure. A useful rule of thumb: if you could still hold a normal conversation over it without raising your voice, you are in a sensible range.

Placement matters less than usual. Low frequencies are far less directional than high ones, so a speaker on the floor, behind a chair or on the far side of the room works about as well as one beside your head. This is the opposite of the advice you would give someone using white noise, where the source position is very audible.

All night or on a timer. The web player generates sound continuously and free sessions run for 30 minutes, which is enough to fall asleep to but not enough to run overnight. The Android app removes the session limit and adds a sleep timer, offline playback and background play, which is the setup most people end up wanting once they have decided the sound suits them.

How It Compares With the Other Colours

Brown noise sits at one extreme of the spectrum of noise colours, and the useful way to think about the others is as a slider from dark to bright. Pink noise at −3.07 dB per octave is the halfway house: still warm, but with the detail brown noise throws away. White noise is flat, bright and by far the most studied. Green noise concentrates on the middle and drops both extremes, which makes it the one colour that sounds much the same on a phone speaker as on headphones. Blue noise tilts the other way entirely at +3.08 dB per octave, and is best understood as an engineering signal rather than a sleep sound.

If your problem is rumble, start here. If your problem is voices, start with green or white. If you are not sure, pink is the safest default.

Frequently Asked Questions

Related pages

• Brown Noise for Sleep — The free web player, plus the full guide to brown noise for sleep, focus, and tinnitus.
• Pink Noise — Equal energy in every octave, measured at −3.07 dB per octave — the natural-sounding default and the audio industry's calibration signal.
• White Noise — The flat reference colour, measured at 0.00 dB per octave — the best of the five at making speech unintelligible.
• Green Noise — The mid-frequency colour — a pink base with a broad 500 Hz emphasis, and the only one of the five with no standard definition.
• Blue Noise — The bright end of the spectrum at +3.08 dB per octave — an engineering signal that is genuinely useful against high-pitched noise, and a poor choice for sleep.
• Brown Noise for Tinnitus — Masking versus habituation, why the pitch of your tinnitus decides the colour, and where sound therapy actually sits in the 2014 clinical guideline.
• Brown vs White Noise — The widest gap on the site — 5.98 dB per octave, about 38 dB apart by 8 kHz — and what each colour can and cannot cover as a result.
• Brown vs Pink Noise — 2.91 dB per octave apart — indistinguishable in the bass, nineteen decibels apart at the top, and one of them collapses on a phone speaker.
• Brown Noise for ADHD — The 2024 meta-analysis with its real numbers — a small benefit on lab attention tasks in ADHD, a negative effect without it, and zero studies of brown noise.
• Brown Noise for Focus — Why concentration is a masking problem measured in speech intelligibility, and why brown noise beats every colour for rumble but loses to white for voices.
• Brown Noise for Babies — The 2014 Pediatrics measurements first: all fourteen infant sleep machines tested exceeded the nursery noise limit at 30 cm, and what that means for level, distance and duration.
• Brown Noise App — Which brown noise app to install, whether it is really free, and the five things an installed app does that a browser tab is not allowed to.