Green Noise

The mid-frequency colour: no rumble underneath, no hiss on top. Also the only one of the five with no agreed definition — so here is exactly how this one is built.

First, the Honest Part: Green Noise Is Not Standardised

White, pink and brown noise have precise definitions. Each one names a specific slope — 0, −3 and −6 decibels per octave — and any two implementations that follow the definition will sound essentially identical. Green noise has nothing of the kind. There is no standards body definition of green noise in audio, no agreed slope, and no agreed centre frequency. Two apps offering "green noise" can be producing genuinely different sounds, and neither is wrong, because there is nothing to be wrong about.

The common description — the one nearly every page repeats — is that green noise is the mid-frequency component of white noise, centred somewhere around 500 Hz, and said to resemble the ambient background of the natural world. That description does have a real origin, though not the one you would expect. In signal processing, Lau, Arce and Gallagher's Green-noise digital halftoning (Proceedings of the IEEE, 1998; 86(12):2424–2444) introduced green noise precisely as the mid-frequency component of white noise — as a printing technique, for arranging dots on paper. The audio usage borrowed the mid-frequency idea from an image-processing paper and gave it a nature metaphor.

So when you compare green noise between apps, you are comparing interpretations rather than implementations of a standard. Which is why the next section describes this one in full.

Exactly How This Player Builds It

The interpretation used here is a broad mid-frequency emphasis, not a resonant peak. It is built as: a pink noise foundation at −3 dB per octave; a wide +8 dB bell centred at 500 Hz with a Q of 0.7, which is roughly two octaves across; two cascaded 100 Hz high-pass filters to pull back the rumble; and a 6 kHz low-pass to pull back the hiss.

Measured on the output, the third-octave peak lands in the 400–500 Hz bands, with gentle skirts of roughly 6 dB per octave either side rather than a narrow resonance. The result stays pink-like in character — a broad tilt toward the middle, not a filtered whistle or a honk. If you have heard "green noise" elsewhere that sounded like a band-passed hiss with an obvious resonant character, that was a different and much narrower interpretation of the same word.

Because green noise is a shaped signal rather than a pure slope, there is no single dB-per-octave figure to quote for it the way there is for the other four. Quoting one would be dishonest. What can be stated is the shape, the centre frequency, the bell width and the filter corners, which is what is above.

As with the rest of the set, the output is normalised to −20 LUFS by ITU-R BS.1770-4 K-weighting so switching colours does not change perceived loudness, and the two channels come from independent random sequences so the stereo image is genuinely decorrelated.

What Green Noise Sounds Like

Nature ambience with both extremes taken off. A stream heard from a few metres back rather than from the bank. A forest in light wind, without the individual leaves. The hush of a large room with a fan somewhere in it. There is no thunder underneath and no hiss on top; what is left is the middle, and the middle is where most of the sound of the outdoors actually lives.

Played immediately after brown noise it sounds like someone opened a window. Played immediately after white noise it sounds like someone closed one. That in-between quality is the whole point: it is the colour for people who have decided brown noise is too muffled and white noise is too harsh, which turns out to be a lot of people.

It is also, subjectively, the least noise-like of the five. Brown and white both sound generated. Green noise sounds more like a place.

What Green Noise Is Genuinely Good At

Phone and laptop speakers. This is green noise's real advantage and it is a practical one. Small speakers roll off steeply below 200–300 Hz, which destroys brown noise, and cheap drivers often have a spiky, unpleasant top end, which makes white noise worse. Green noise deliberately contains almost nothing below 100 Hz and almost nothing above 6 kHz — the two regions small hardware handles worst. It is the one colour on this site that sounds substantially the same through a phone speaker as through headphones. If you do not want to sleep in headphones and do not own a good speaker, start here.

The middle ground between brown and white. If you have tried both and found brown noise too heavy and white noise too sharp, green noise is a more useful next step than pink, because it does not merely sit between them on a slope — it removes both of the things you objected to.

Covering the body of speech. The 300–800 Hz region that green noise emphasises is where vowel fundamentals and the general presence of a voice live. Green noise takes conversation from "someone is talking in the next room" toward "there is a room next door", which for many people is the part that pulls attention.

Daytime background. It is unobtrusive in a way brown noise is not — brown noise announces itself with weight, and green noise mostly just occupies the room.

What Green Noise Is Bad At

Both ends of the spectrum, by construction. Everything below 100 Hz and above 6 kHz has been deliberately removed. That means green noise does essentially nothing against traffic rumble, HVAC, footsteps overhead or a neighbour's bass — use brown noise. And it does essentially nothing against coil whine, a squealing fan or other high-pitched intrusions — use white or blue noise. Green noise is specialised, and the specialisation cuts both ways.

Consonants, and therefore full speech masking. It covers the body of a voice but leaves the 2–4 kHz consonant band largely untouched, and consonants are what make speech intelligible. If you can still make out individual words through it, that is why, and white noise is the correct fix.

Voice calls and speaking aloud. The frequencies green noise emphasises are the same frequencies your own voice occupies most strongly. Some people find it feels like it is competing with them when they are talking, reading aloud or on a call, in a way that brown noise never does.

Evidence, entirely. This is not a case of thin research; there is none. No study has tested green noise for sleep, focus, tinnitus or anything else, and none realistically can while the term has no agreed definition — there would be nothing consistent to test. The 2021 systematic review of noise as a sleep aid covered continuous white noise and similar broadband noise and rated the overall evidence very low quality; green noise did not appear in it at all. Anyone claiming clinical support for green noise specifically is making it up. Nothing here is medical advice.

Using It Well

Test it on the speaker you will actually use. Green noise is the colour whose case rests most heavily on hardware, so evaluating it on studio headphones and then deploying it on a bedside phone is testing the wrong thing. If the phone is the plan, judge it on the phone.

Compare it against pink, not against brown. Green noise is built on a pink foundation, so pink noise is its nearest neighbour and the more informative comparison. If pink already sounds right to you, green will sound like pink with the extremes trimmed; if pink sounds slightly hissy, green is the fix.

Web player and app. The browser player runs 30-minute free sessions with nothing to install. The Android app carries green noise alongside brown, white, pink and blue, with no session limit, a sleep timer, offline playback and the option to layer rain or thunder on top of it — which suits green noise particularly well, since it leaves the top of the spectrum free for the rain to occupy.

How It Compares With the Other Colours

Four of the five colours here sit on a single line of spectral tilt: brown at −5.98 dB per octave, pink at −3.07, white at 0.00, blue at +3.08. Green noise is not on that line at all. It is a shape rather than a slope — a hump in the middle with both ends rolled away — which is exactly why it cannot be given a single dB-per-octave figure and why it fills a gap the other four leave open.

Think of it less as a point on the brightness scale and more as a different question: not "how bright do you want it?" but "what if we removed everything except the part you actually hear?"

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.
• Brown Noise — The deepest colour, measured at −5.98 dB per octave — best for traffic rumble and long overnight sessions.
• White Noise — The flat reference colour, measured at 0.00 dB per octave — the best of the five at making speech unintelligible.
• 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.
• Green vs Pink Noise — Green noise here is pink noise plus a 500 Hz bell with both ends cut off — exactly what that chain adds, what it costs, and when the trade is worth it.
• 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 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.