Green noise, and why it sounds like a river.

Green noise is mid-focused broadband noise. Like every noise colour it contains energy across the whole audible range, but the energy is concentrated around the middle — roughly 500 Hz — and rolls away above and below.

That single fact explains everything people notice about it. Human hearing is most sensitive in the mid range, which is also where the natural sounds we find soothing live: a river over stones, steady rain on leaves, wind through a hedge, distant surf. Green noise puts its energy exactly there, so it registers as a sound from somewhere rather than as an electrical hiss. White noise, by contrast, has as much energy at 15 kHz as at 500 Hz, and because our hearing spreads a lot of sensitivity across the top end, it reads as bright and artificial.

A caveat worth having up front: unlike white, pink and brown, green noise has no agreed technical definition. White is flat, pink falls 3 dB per octave, brown falls 6. Green is a description of a shape, not a formula, and different apps implement it differently. Ours is a bandpass centred near 500 Hz, which matches how the term is generally used, but do not be surprised if green noise elsewhere sounds noticeably different. There is no standard to be wrong about.

Masking works by raising the noise floor so that intrusions no longer stand out against silence. Which colour to use follows directly from what you are trying to cover.

Green's mid-range concentration lands close to the human speech band, roughly 300–3,400 Hz. That makes it a reasonable choice in an open office or a shared home, where the disruptive sound is conversation. Intelligible speech is uniquely bad for concentration — considerably worse than non-verbal noise at the same volume, because you cannot help parsing it — so masking that band is worth more than masking anything else.

Where green is a poor fit is low rumble. Traffic, machinery, a neighbour's bass and a snoring partner all live below where green puts its energy, and no amount of volume will fix a colour mismatch. That is brown noise's job.

Be aware that the evidence for any noise colour and focus is thin, and thinner for green than for white or pink simply because green has barely been studied. What research exists on noise and cognition is mixed, with some people helped and others measurably hindered. Treat it as a preference to test rather than a technique to adopt.

Green is a sensible thing to try for sleep, and the reason is comfort rather than evidence. Over a full night, white noise is fatiguing for a lot of people — that top-end energy is exactly what makes a hiss wearing — while brown can feel heavy or pressurising at volume. Green sits between them and, because it resembles moving water, most people stop noticing it quickly. Being forgettable is the single most useful property a sleep sound can have.

What the research supports is narrower than the marketing suggests. There is some work on pink noise and slow-wave sleep, with small samples and promising rather than settled results. On green noise specifically there is essentially nothing, because the term is a recent popular coinage rather than a research category. A 2021 systematic review of noise as a sleep aid concluded the overall evidence is limited and mixed.

So the honest framing is: green noise may suit you better than the alternatives, and that is a real benefit if it means you actually keep using it. But nobody has shown it does anything the others do not.

Keep it quiet. It should blur the edges of the room, not fill it. And if you are running it all night, a speaker is far more comfortable than earbuds — noise needs no stereo separation, so headphones buy you nothing here.

Ordered from the deepest to the brightest:

• Brown — energy falls 6 dB per octave. Deep and rumbling; a waterfall heard from indoors. Best against traffic, machinery and snoring. The most popular for sleep.
• Pink — falls 3 dB per octave, which matches how our hearing weights the spectrum, so it sounds even and natural. Steady rain. The safest default when you do not know what you are masking.
• Green — concentrated in the mid range near 500 Hz. A river, or surf. Good against speech; poor against rumble.
• White — flat across the spectrum, which our ears read as bright and hissy. Untuned radio static. Best against sharp, high intrusions and, like green, against speech.
• Violet (also called purple) — rises 6 dB per octave, the exact mirror of brown. Almost all its energy is at the top. It is harsh to listen to and is rarely used for sleep or focus; its main serious use is in tinnitus masking, where a therapist may match a sound to the pitch of the tinnitus. It is in the player above so you can hear the contrast — start it quiet.

If you want the full decision framework rather than a list, the noise colours guide works through which one to reach for by problem.

One practical point that matters more than the colour: play both green and brown for two minutes each at a low volume, and keep whichever one you stop noticing first. Preference here is idiosyncratic and no amount of theory predicts it.

These are different tools for different problems and it is worth not confusing them.

Noise masks. It raises the floor so external sound stops intruding. It works through speakers, needs no attention, and is comfortable to run for eight hours.

Binaural beats entrain. Two slightly different tones, one per ear, produce a perceived pulse at the difference, which is used to nudge you toward a state. They require stereo headphones — on speakers the two tones mix in the air and the effect vanishes entirely — and are usually run for twenty to thirty minutes.

If your problem is a noisy environment, use noise. If your problem is that you cannot settle in a quiet room, beats are the more relevant tool. Running both is fine and common, but note that a 2025 randomised study found masking sound measurably affects the entrainment response — so if you are trying to work out whether beats do anything for you, test them without noise underneath first.

You can try beats free in the browser generator, no signup, alongside this player.

Volume is the only real risk. Noise is a background, not a foreground. If you can hold a conversation over it comfortably, you are in the right range. Sustained loud audio damages hearing regardless of what is playing, and running something all night makes that exposure long.

Infants need different rules. Do not apply adult judgement here. Paediatric guidance sets lower limits and a minimum distance from the cot, and infant hearing is more vulnerable than adult hearing. Follow that guidance rather than a website — including this one.

Tinnitus deserves a professional. Sound therapy is a legitimate clinical approach, but the right sound is individual and matching it is something an audiologist does with you. Violet noise in particular gets recommended casually online for tinnitus; please do not self-prescribe it. Our tinnitus page covers why.

If it stops helping, stop. Some people find that relying on noise makes quiet rooms harder to sleep in over time. If you notice that, it is worth tapering rather than escalating the volume.