What is green noise? How it sounds next to brown and white
Green noise sits in the middle of the audible range: duller than white noise, thinner and more open than brown noise, and no standards body defines it. Slo plays all three free in the browser at slonoise.com, one tap apart, and its green noise puts 52.2% of its power between 250 Hz and 4 kHz against 15.6% for its white noise.
What green noise does not solve
It adds sound to a room and removes none. A green-noise track never quietens the neighbour’s television, and it does no soundproofing. Because the label carries no agreed spectrum, two providers can ship different signals under the same name, so a recommendation you read elsewhere may not describe the file you end up playing. And nothing here says green noise will help you sleep, because no published trial has tested it.
No standards body has defined it
White noise and pink noise have standard entries. The ASA/ANSI acoustical terminology database, which the Acoustical Society of America maintains, defines white noise at entry 2.37 as “noise for which the spectrum density or spectrum level is independent of frequency over a specified range”, and pink noise at 2.38 as “noise for which the spectrum density varies as the inverse of frequency”.
Ask the same database for green noise and the page 404s. Brown noise and red noise return 404 too, which is worth knowing before anyone tells you the colours carry equal authority. Checked 10 September 2026.
That absence has a practical consequence. Hand an engineer a slope for pink noise, minus 3 dB per octave, and they will build the signal you agreed on. For green noise there is nothing to hand over, so the word describes a listening impression and a marketing category rather than a signal.
Where the 500 Hz figure comes from
Most descriptions of green noise put the emphasis in the middle of the spectrum, around 500 Hz. That number traces back to ambient sound-effects catalogues, where the word green labelled recordings meant to stand in for outdoor background without traffic or machinery. It has never appeared in a standard, and it does not describe every file sold under the name.
Slo’s own green noise does not sit at 500 Hz either. The generator runs a one-pole lowpass over a white source and mixes a little raw white back in, which weights the result towards the middle without putting a peak anywhere. Its power-weighted mean frequency measures 3,494 Hz. Read the label as a rough family, then judge the recording.
The measured band split
These numbers come out of this site’s own code, measured on 4 September 2026. Each colour ran for 30 seconds at 48 kHz mono through slo-noise-worklet.js, and an averaged 8192-point Hann FFT gave the spectrum. Band shares give the fraction of total power under 250 Hz, in the middle band up to 4 kHz, and above 4 kHz. Loudness gives the integrated EBU R128 figure at the generator’s default level.
| Sound | Power below 250 Hz | Power 250 Hz to 4 kHz | Power above 4 kHz | Mean frequency, Hz | Loudness, LUFS |
|---|---|---|---|---|---|
| Green noise | 25.2% | 52.2% | 22.6% | 3,494 | −15.9 |
| Brown noise | 65.9% | 31.7% | 2.3% | 537 | −15.5 |
| White noise | 1.0% | 15.6% | 83.4% | 12,026 | −11.5 |
| Pink noise | 52.5% | 28.8% | 18.7% | 2,511 | −17.4 |
Green noise holds the only middle-band share above half, which gives the honest version of the mid-range claim. It also keeps 22.6% of its power above 4 kHz, so it does not sound warm; next to brown noise you will hear air in it.
Two limits on the table. The figures describe Slo’s generators rather than green noise everywhere, and a rival app may measure differently under the same name. A share of power also differs from what you hear: your speakers, your headphones and your own hearing all reshape it, which explains why the listen card sits above the table.
Does green noise help you sleep?
No controlled study of green noise exists. A PubMed search for the exact phrase “green noise” together with “sleep” on 10 September 2026 returned zero papers. Any article claiming that research supports green noise has borrowed its results off a different signal.
The evidence nearby covers other colours. The World Health Organization’s 2018 environmental noise guidelines establish that environmental noise can disturb sleep, and that removing the source beats covering it wherever you can. Riedy and colleagues reviewed the human studies of continuous noise in 2021 and rated the evidence very low quality with mixed results, so nobody can promise that even white noise helps. Green noise sits one step further out than that.
Treat it as a preference. Play it, keep it if the room feels easier, drop it if it turns into one more thing to listen to.
Where green noise fits
| Situation | Try green noise? | Why |
|---|---|---|
| White noise hiss tires you | Yes | Green noise drops the high band to 22.6% |
| Brown noise feels heavy or muddy | Yes | Green noise keeps 22.6% of its power above 4 kHz |
| Traffic rumble through a wall | No, try brown | Brown noise carries 65.9% of its power under 250 Hz |
| Typing and voices next door | No, try white | White noise puts most of its energy where speech edges live |
| Small phone speaker, no headphones | Yes | Mid-weighted content survives a small driver better than deep bass |
| You want a documented spectrum | No | Pick pink or white noise, which carry standard definitions |
A noise generator with live spectrum controls sits on the roadmap at /tools/noise-generator/, which will let you shift the balance yourself instead of picking a colour name. Until it ships, the browser mixer comes closest: layer green noise under river or rain and set the two levels on their own.
Listen at a sensible level
Set the volume to the lowest point where the sound still does its job. A phone at 50% does not mean 50 dB, and the same setting sounds louder through in-ear headphones than through a speaker across the room. The WHO advises adults to keep average personal-audio exposure below 80 dB and to shorten listening time as the level goes up. Keep alarms, doorbells and the people in your home audible.
Questions people ask
What green noise is good for
A steady background in the middle of the audible range, duller than white noise and lighter than brown noise. People play it for sleep, for reading and in quiet rooms. No study has tested it for any of those, so treat it as a listening preference.
Does green noise help you sleep?
Nobody knows. A PubMed search for green noise and sleep on 10 September 2026 returned zero papers. The nearest evidence covers white noise, and a 2021 systematic review rated that evidence very low quality.
What does green noise do?
It adds a steady mid-range sound to the room, which can make a sudden noise less distinct. It cancels nothing, and it changes nothing about what reaches your ears through the wall.
Does green noise harm your hearing?
The level matters more than the colour. The WHO advises adults to keep average personal-audio exposure below 80 dB and to listen for less time as the level rises. Use the lowest setting that still does the job, and keep alarms audible.
Read next
- Brown noise vs white noise covers the two colours green noise sits between.
- Noise colours explained runs through blue, violet and grey as well.
- Brown vs white vs pink noise adds the third standard colour.
- Green 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. Green noise, brown noise and red noise return 404.
- 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 measurements in
src/data/sound-measurements.ts, taken 4 September 2026 against the shipped generator.
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.
