What is red noise? It's another name for brown noise
Red noise is another name for brown noise: a deep, steady rumble with almost no hiss in it, the sound of a waterfall heard from a long way off. If an app or a paper hands you red noise, that rumble is what you get. You can play it free in a browser at slonoise.com, where it’s listed under the brown noise name and needs no sign-up. People reach for it to cover a truck idling at the curb, the boiler downstairs or bass coming up through the floor, and it’s the most played sound on the site.
Red noise vs brown noise
In audio the two words point at the same signal, and which one you meet depends on who wrote the label. Brown came first, and not from the color. It came from Brownian motion, the aimless jiggling of pollen particles in water that the botanist Robert Brown described in 1827. Sound that wanders the same way keeps most of its power down in the deep end of what you can hear. Red came from the light analogy that already gave us white and pink noise, because red light sits at the low-frequency end of the rainbow.
Neither name has a standard behind it. The acoustical terminology database run by the Acoustical Society of America has an entry for white noise and one for pink noise; look up brown noise or red noise and you get nothing, checked on 10 September 2026. So when an app lists red and brown as two different sounds, nothing official says they differ. Play both and trust your ears.
If you want the number: climb an octave, from any pitch to the one twice as high, and red noise carries about a quarter of the power it had below, a drop of roughly 6 decibels. That steep fall is the whole reason it rumbles instead of hissing.
What does red noise sound like?
It’s a deep, soft roar. There’s no hiss over it and nothing sharp to catch your ear. Listeners compare it to a distant waterfall, or to the cabin of a plane three hours into a flight.
Hearing it beside the other two colors takes about twenty seconds. Play these at the same volume, one after another.
In our own measurements from September 2026, red noise puts about two thirds of its power into the deepest part of your hearing and barely 2% up at the top. White noise does the reverse, which is why it hisses. Pink noise sits between the two, and of the three it comes closest to the background of an ordinary room.
That balance decides what each one covers. Red noise is the best of the three at covering traffic rumble and machinery. Voices through a wall blur better under pink or white, because the consonants that carry the words are higher pitched, and no sound removes a voice at all: the brain keeps hunting for speech inside noise, so the best you get is words too smeared to follow. The brown, pink and white comparison takes that apart properly.
What sound does the color red make?
A color makes no sound by itself. The colors in white, pink and red noise are borrowed from light, not from anything you can see while the sound plays. Red light has the lowest frequency your eye picks up, so engineers reached for it to name the noise that piles its power at the low end of hearing. Follow the analogy through and the sound the color red makes is that deep rumble; press play above and you are hearing it.
People ask the same thing about green and blue. Same borrowed idea, and noise colors explained runs through the whole set.
What people use red noise for
Most people use it to cover a low, steady nuisance: a bus braking at the stop outside, the boiler coming on before dawn, a fridge humming in the next room, bass through the wall from a neighbor’s TV. All of that sits in the same deep range red noise fills, so it stops standing out.
It also gets left on during work and reading, for the reason a fan does: one dull unchanging sound is easier to ignore than a room that keeps producing single noises. Whether that helps you or nags at you is personal, and a week of evenings is long enough to find out.
It won’t make you sleepy, though, and it won’t block the conversation next door. For voices, white noise or pink noise reaches further up the pitch range and does more.
Does red noise help you sleep?
Nobody has tested red or brown noise on its own for sleep. The nearest evidence covers steady sound in general, and when Riedy and colleagues gathered that work in 2021 they found it pointing in opposite directions, with some people sleeping better and others sleeping worse. Their verdict on the evidence itself was that it’s very weak. The World Health Organization’s noise guidelines make a point that matters more in practice, which is to quiet the source where you can, since a closed window beats any recording.
Test it as a preference, then. Keep the volume low enough that you could talk across the room without raising your voice, put the speaker away from your pillow rather than beside your head, and give it several nights before you decide. The deep end brings one catch worth knowing: a phone speaker cannot produce it, so you turn the volume up and still barely hear anything. Earbuds, or a small speaker on a shelf, handle it far better at a lower setting. The WHO’s advice on personal audio is to stay under 80 dB on average, and to listen for less time as the level climbs.
Red noise in a research paper
Outside audio the word stretches. In climate science and other work on time series, red noise means a signal where each value leans on the one before it, so it drifts slowly instead of jumping around. It need not follow that steep one-quarter-per-octave slope at all. Torrence and Compo’s guide to wavelet analysis uses it as the background a real climate signal has to rise above. In a sleep or focus app, red noise means the rumble.
Questions people ask
Is red noise the same as brown noise?
In audio, yes. Both words point at the same signal. One name came from Brownian motion and the other from red light, and no standards body defines either. If an app sells them as two separate sounds, play both and judge by ear.
What does red noise sound like?
A deep, soft roar with almost no hiss, close to a distant waterfall or the cabin of a plane at cruise. It covers low sounds such as traffic rumble well, and voices through a wall much less well.
What sound does the color red make?
A color makes no sound by itself. Noise colors are borrowed from light: red light sits at the low-frequency end of what your eye sees, so red noise became the name for sound weighted toward the deep end of what your ear hears.
What is red noise good for?
People use it to cover a low, steady nuisance: traffic, a boiler, a fridge, bass through the floor. Some also leave it on while they work, because one dull unchanging sound is easier to ignore than a quiet room with occasional bangs in it.
Does red noise help you sleep?
No study has tested it on its own. When researchers gathered the work on steady sound in 2021, the findings pointed both ways and they judged the evidence very weak. So treat red noise as a preference: keep the volume low and give it a week.
What does red noise mean in science?
In climate science and other work on time series it means a signal where each value leans on the one before it, so it drifts slowly instead of jumping around. That definition does not require the steep drop in power that audio red noise has.
Read next
- Brown noise vs white noise compares the rumble with the hiss.
- What is green noise covers the mid-range color with no standard definition.
- Noise colors explained has the entries for blue, violet and grey.
- Brown noise for sleep opens the bedtime preset with a timer.
Sources
- White noise, entry 2.37 and pink noise, entry 2.38, ASA/ANSI Standard Acoustical and Bioacoustical Terminology database. Brown noise and red noise return 404.
- Torrence C, Compo GP (1998), A Practical Guide to Wavelet Analysis, Bulletin of the American Meteorological Society 79(1).
- World Health Organization (2018), Environmental Noise Guidelines for the European Region.
- Riedy and colleagues (2021), Noise as a sleep aid: A systematic review.
- World Health Organization, Deafness and hearing loss: Safe listening.
- First-party: band shares measured from Slo’s own noise generators,
src/data/sound-measurements.ts, 4 September 2026.
Explore more sounds in Slo
Stack two or three sounds, keep the blend, and let the timer stop it. Slo, on iOS, Android and Mac.
