Brown Noise, Green Noise, White Noise: What the Colours Actually Mean

Short answer: noise colours describe how sound energy is distributed across frequencies. White noise spreads energy evenly, so it sounds bright and hissy. Pink and brown noise put progressively more energy into low frequencies, so they sound deeper, like rain or distant surf. Green noise is not a formal engineering term at all. For sleep, pink and brown are the ones most people prefer, and the research supporting any of them is weaker than the internet suggests.

That last sentence is the one worth sitting with. Roughly 175,000 people a month search these terms, and almost every page they land on is more confident than the evidence justifies.

The colours are real physics

This is not wellness vocabulary borrowed from crystal healing. Noise colours come from signal processing, and they describe spectral density, how power is distributed across the frequency range.

The convention works in decibels per octave. Each time frequency doubles, the energy either stays flat or drops by a fixed amount:

A quirk of human hearing matters here. We perceive frequency logarithmically, but white noise distributes energy linearly. The octave from 10,000 to 20,000 Hz contains as much energy as everything below 10,000 Hz combined, which is why flat-spectrum white noise sounds far harsher than "equal energy everywhere" would imply. Pink noise corrects for this, which is why it sounds balanced to us despite having a sloped spectrum.

White noise

Equal power at every frequency. It is the most effective at masking sudden sounds across the whole range, which is why it is standard in hospitals and offices, and why it works well against a snoring partner or traffic.

The cost is that it is tiring. Most of its perceived energy sits in the high frequencies, and several hours of that is unpleasant for many people. If you have tried white noise and found it grating, you were not doing it wrong. That is simply what a flat spectrum sounds like to a human ear.

Pink noise

Energy drops 3 dB per octave, which offsets our logarithmic hearing almost exactly. The result sounds neutral and natural. Steady rain is close to pink noise. So is wind in trees, and much of the ambient sound of a forest.

Pink noise also has the most interesting research behind it, though "most interesting" is doing some work in that sentence. Papalambros and colleagues (2017) delivered 50-millisecond pulses of pink noise, phase-locked to the up-state of each slow oscillation during sleep in older adults. Overnight word recall improved by around 27%, against roughly 6% in the sham condition.

Now note what that required: EEG monitoring, an algorithm detecting each slow wave in real time, pulses fired within milliseconds of the right moment, a laboratory, and thirteen participants in a crossover design.

That is not playing a pink noise track from your phone all night. It is close to the opposite, brief, precisely timed pulses rather than continuous sound. Any page citing this study as evidence that pink noise playback deepens sleep has either not read it or is hoping you will not.

Brown noise

Named after Brownian motion rather than the colour, from the same random-walk mathematics that describes pollen drifting in water. Energy drops 6 dB per octave, so the high end is heavily attenuated and what remains is deep and rumbling.

Brown noise has become the most-searched of all the colours, largely through people describing it as the first sound that made their thoughts go quiet. There is a substantial online community, particularly among people with ADHD, reporting that it helps them focus.

Be careful with how that gets reported. Self-report from an enthusiastic community is a real signal about preference, and it is not evidence of a clinical effect. Controlled research specifically on brown noise is thin. If brown noise helps you, it helps you. That is a good enough reason to use it. It is not a good enough reason for a website to tell you it treats anything.

Green noise

Here the story diverges from the others, and honestly.

Green noise is not a standard term in acoustics. There is no agreed slope, no engineering definition, no entry in the reference literature alongside white, pink and brown. What exists in practice is a marketing label applied to noise concentrated in the middle of the spectrum, around 500 Hz, sold as "the sound of nature."

Which is fine as a product. Mid-frequency-weighted noise sounds pleasant, and if a track labelled green noise helps you sleep, keep using it.

What is not fine is the claim cluster that has grown around it. You will find pages asserting that green noise aids digestion, balances the nervous system, or corresponds to a particular chakra. There is no research supporting any of it, because there is no defined thing to research. The 41,000 people a month searching "green noise" are mostly being sold a pleasant sound with an invented backstory.

What the research actually supports

A fair summary, stated plainly:

Masking works. This is well established and not really in dispute. Continuous background sound reduces the salience of sudden noises, and sudden noises cause arousals during sleep. If your sleep is disrupted by traffic, neighbours or a snoring partner, noise of any colour will help. That is an acoustics finding, not a wellness one.

The evidence for improving sleep in a quiet room is very weak. The most thorough assessment is Riedy, Smith, Rocha and Basner's 2021 systematic review in Sleep Medicine Reviews, covering 38 studies. Graded formally, they concluded that the quality of evidence for continuous noise improving sleep was very low, and stated plainly that this "contradicts its widespread use."

They went further, noting that continuous noise "may also negatively affect sleep and hearing." That is the current state of the field, from the people who read all of it.

Colour preference is preference. No good study demonstrates that brown outperforms pink, or pink outperforms white, for sleep in general. What varies is which one people find tolerable for eight hours, and that varies a lot between individuals.

There is a plausible downside. Some researchers have raised concerns that all-night sound exposure could interfere with the auditory system's own overnight recovery, and that habituation might make sleeping in silence harder over time. This is not established either, but it is a reason to treat "leave it on every night forever" as an open question rather than an obvious good.

The quality of evidence for continuous noise improving sleep was very low, which contradicts its widespread use.

Riedy, Smith, Rocha & Basner, Sleep Medicine Reviews, 2021

Using it sensibly

Volume is the part that matters most. Keep it low. Comfortably below normal conversation, at the level where it fades into the background rather than commanding attention. Sound machines have been measured producing levels loud enough to raise real concern, particularly when placed close to a sleeper. Louder is not more effective at masking; it just adds its own disturbance.

Distance beats volume. Place the source across the room rather than beside your head. Same masking, less exposure.

Use a continuous loop, not a short one. A three-minute file that restarts audibly is worse than useless. The seam becomes exactly the kind of sudden change you were trying to mask.

Match colour to problem. Sharp intermittent noise from outside: white or pink, because you need coverage in the high frequencies where those sounds live. Low rumble from traffic or a neighbour's bass: brown, because that is where the energy is.

Your phone is enough. A dedicated machine buys you convenience and a better speaker. It does not buy you a different physical phenomenon. Start with a free app before spending anything.

Who should be more careful

Infants and young children. Their hearing is more vulnerable, and sound machines are often placed in cots. Keep the device well away from the child, keep the volume low, and do not run it continuously all night.

Anyone with tinnitus. Masking sound helps some people with tinnitus considerably and makes it worse for others. If you have tinnitus, this is worth discussing with an audiologist rather than experimenting alone.

If you already sleep well in silence. Then there is no problem to solve, and adding a nightly sound habit is a change with unclear long-term effects and no upside.

Questions people ask

Is brown noise better than white noise for sleep? No study supports that as a general claim. Brown is easier on the ears over long periods because it has less high-frequency energy, which is why more people tolerate it all night. That is a preference difference, not a performance difference.

Is green noise a real thing? Not as an acoustics term. It is a marketing label for mid-frequency-weighted noise. The sound is real; the technical framing around it is not.

Can I run noise all night, every night? Most people do without obvious problems. The honest position is that long-term effects have not been well studied, so low volume and some nights off is the prudent approach.

Does any of this help with focus rather than sleep? There is real evidence here, and it is narrower than the enthusiasm. A 2024 meta-analysis of 13 studies found a small benefit of white or pink noise on task performance in young people with ADHD (g = 0.25), alongside negative effects in groups without ADHD. So it may help some people concentrate and actively hinder others.

This article covers sleep and hearing for general information and is not medical advice. Persistent insomnia, tinnitus or daytime sleepiness are worth discussing with a clinician rather than treating with a sound app.