White, pink and brown noise are all random, steady sounds; the difference is how their energy is spread across frequencies. White noise has equal power at every frequency, so it sounds bright and hissy. Pink noise loses 3 dB of power per octave, which gives every octave equal energy and a softer, rain-like sound. Brown noise loses 6 dB per octave, so it is dominated by low frequencies and sounds like a deep rumble. Which one is "best" is mostly personal preference.
- White noise: flat power spectrum (equal energy per hertz). Sounds like TV static or a hissing radio.
- Pink noise: power falls by 3 dB per octave (1/f), so each octave carries equal energy. Sounds like steady rain or wind.
- Brown noise: power falls by 6 dB per octave (1/f²). Named after Robert Brown and Brownian motion, not the colour. Sounds like a waterfall or distant thunder.
- "Green noise" is not a standard scientific term; it is a popular name for noise concentrated in the middle of the audible range.
- Evidence for sleep and focus benefits is mixed and mostly modest. The most reliable effect is masking: steady sound makes sudden noises less noticeable.
- Keep the volume low, especially for all-night listening.
What are noise colours?
A noise colour is a shorthand for the shape of a random signal's power spectrum, meaning how much energy it has at low, middle and high frequencies. The names borrow loosely from light: white light contains all visible wavelengths in roughly equal measure, so a sound with equal power at all frequencies was called white. Other colours were then named by analogy, with "pinker" or "redder" noise having more energy at low frequencies and "bluer" noise more at high frequencies.
All of these sounds are random, with no melody or rhythm, but their overall character stays constant. That steadiness is what makes them useful for covering up other sounds.
One detail explains most of the confusion. Our hearing works in octaves, each a doubling of frequency. The octave from 1,000 to 2,000 Hz spans 1,000 Hz, while 100 to 200 Hz spans only 100 Hz, so a sound that is "flat" per hertz is not flat to the ear: it piles up energy in the treble.
White vs pink vs brown noise at a glance
| Colour | Spectrum | Slope per octave | Sounds like |
|---|---|---|---|
| White | Equal power per hertz (flat) | 0 dB | Static, hiss, a detuned radio, a hair dryer |
| Pink | 1/f: equal power per octave | −3 dB | Steady rain, wind, rustling leaves |
| Brown (red) | 1/f² | −6 dB | Waterfall, distant thunder, aircraft cabin hum |
| Blue | Rises with frequency (f) | +3 dB | Very bright hiss, spraying water |
| Violet (purple) | Rises with f² | +6 dB | Sharp, high hiss |
| "Green" | Not standardised; energy concentrated in the mid range | – | Soft, nature-like ambience |
White noise: flat and bright
White noise has a flat power spectral density: every hertz of bandwidth carries the same amount of power. Because each higher octave contains twice as many hertz as the one below, each octave of white noise carries twice the energy of the previous one, which is a rise of about 3 dB per octave when you measure in octave bands. That is why white noise sounds bright and hissy rather than balanced.
The bright character makes white noise good at covering voices and sharp, sudden sounds, and engineers use it to test electronics and audio equipment. Many people find it harsh for long listening; others like its "wall" of sound. Try our white noise generator, which plays in your browser with a sleep timer.
Pink noise: balanced and rain-like
Pink noise has a power spectral density proportional to 1/f, which means power falls by about 3 dB for every doubling of frequency. The result is equal energy in every octave, which matches how we perceive pitch, so pink noise tends to sound even and natural rather than hissy. It is also called 1/f or flicker noise.
Audio engineers use pink noise to check and tune speakers and rooms because an octave-band analyser shows it as a flat line. Listeners compare it to steady rain or wind, and it is the colour most often used in sleep research. Listen to our pink noise generator and compare it with white noise at the same volume.
Brown noise: deep and rumbling
Brown noise, also called Brownian noise or red noise, has a power spectral density proportional to 1/f², so power falls by about 6 dB per octave. The name comes from Brownian motion, the random jiggling of particles first described by the botanist Robert Brown: if you add up a white noise signal step by step (a random walk), you get brown noise. It has nothing to do with the colour brown.
With most of its energy in the bass, brown noise sounds like a strong waterfall, heavy surf, distant thunder or the drone inside an aircraft. Many people find it the most soothing of the three because it has very little hiss. It covers low, rumbling noises such as traffic well, and high-pitched sounds less well. Our brown noise generator includes a tone control if you want it a little brighter.
Blue, violet, grey and "green" noise
- Blue noise rises by 3 dB per octave (power proportional to f). It is mainly used in image processing and printing, where blue-noise dithering spreads out patterns so they look smoother, and rarely for listening.
- Violet (purple) noise rises by 6 dB per octave. It is used in audio dithering and appears in some sound-therapy apps, but most people find it very sharp.
- Grey noise is white noise reshaped by an equal-loudness curve so that it sounds roughly equally loud at all frequencies to an average listener.
- Green noise has no agreed scientific definition. In apps and videos it usually means noise concentrated in the middle frequencies, often described as sounding like nature. Our green noise page follows that popular meaning.
Everyday steady sounds also work as coloured noise. A fan or air conditioner is broadly brown-to-pink with a hum, rain sits close to pink, and ocean waves rise and fall like slowly modulated brown noise.
Does coloured noise actually help with sleep or focus?
The honest answer is: sometimes, a little, for some people. The research is mixed, many studies are small, and the quality of the evidence varies. Coloured noise is a comfort tool, not a treatment.
Masking: the best-supported effect
Your brain reacts more to changes in sound, such as a door slamming, than to the absolute level. A steady background sound raises the floor, so sudden noises stand out less and are less likely to wake or distract you.
Sleep
Some studies report that people fall asleep faster or wake less often with continuous noise, particularly in noisy environments, while others find little or no effect. Reviews of the research have generally rated the evidence as low quality. Small laboratory studies that play short bursts of pink noise timed to deep-sleep brain waves have reported stronger slow-wave activity, but that technique needs special equipment and is not the same as a noise track running all night.
Focus and attention
Steady noise helps some people concentrate in noisy places, mostly by covering speech. A few studies have reported small improvements in attention tasks for some people with attention difficulties, and no benefit or a negative effect for others. Brown noise's popularity for focus is ahead of the evidence: use it if it helps, and try silence or quiet music if it does not.
Tinnitus
Some people find gentle background sound makes tinnitus less noticeable, and audiologists may suggest sound therapy as part of a wider plan, but noise does not cure it. If you have new, one-sided or worsening tinnitus, see a doctor or audiologist.
How to choose the right noise
- Start with what you need to cover. Voices, a TV or high-pitched sounds: try white or pink noise. Traffic, bass from music or a rumbling boiler: try brown noise.
- Compare at the same volume. White noise sounds louder than brown noise at the same setting because our ears are most sensitive to upper-middle frequencies.
- Listen for a few minutes. A sound that seems pleasant at first can become tiring; pink and brown noise tend to be easier to tolerate for long periods.
- Try natural sounds too. Rain, waves or a fan offer similar masking with more variety. Our sleep sounds mixer lets you layer rain, waves, wind and noise and save your mix.
- Use a timer or fade-out if you only need help falling asleep, or leave the sound on all night at a low level if waking in silence bothers you.
All our noise and nature sounds are listed on the sleep and relaxation hub. They are generated live in your browser, so nothing is uploaded or recorded.
How loud should noise be?
Quieter than you think. Use the lowest level that covers the sounds that bother you; for sleep, that is usually below the level of a normal conversation. The World Health Organization's safe listening guidance for adults treats about 80 dB for up to 40 hours a week as a reference limit, and much less time is safe as the level rises, so a noise track that runs for eight hours every night should stay well below that.
- Place a speaker across the room rather than next to your head, and prefer it to earbuds for all-night listening.
- If you notice ringing, muffled hearing or need to keep turning the volume up, turn it down and give your ears a rest. You can check your hearing with our online hearing test, which is a screening aid, not a diagnosis.
- For babies, take extra care with volume and distance; our white noise for babies page includes safe-volume tips.
Frequently asked questions
What is the difference between white, pink and brown noise?
The balance of low and high frequencies. White noise has equal power per hertz and sounds hissy, pink noise has equal power per octave and sounds like rain, and brown noise has most of its power in the low frequencies and sounds like a deep rumble.
Which noise colour is best for sleep?
There is no single best colour. Pink noise is the most studied, brown noise is popular because it has little hiss, and white noise masks voices well. Try each at a low volume and choose the one you find easiest to ignore.
Why is it called brown noise?
After Brownian motion, named for the botanist Robert Brown. Brown noise can be made by summing white noise into a random walk, the same mathematics that describes Brownian motion. It is also called red noise, by analogy with red light's lower frequencies.
Is green noise real?
Not as a scientific term. "Green noise" is a popular label for noise concentrated in the middle frequencies, often described as sounding like nature. Different apps make it differently, so two green noise tracks can sound quite different.
Is it bad to sleep with noise on all night?
Not for most adults, provided the volume is low and the speaker is not right beside your ear. If you would rather not rely on it every night, use a sleep timer with a fade-out so the sound stops after you fall asleep.
Does brown noise help with ADHD?
Some people with ADHD say steady noise helps them focus, and a few small studies report modest effects, but results are inconsistent and noise is not a treatment. It is safe to try at a low volume alongside any advice from a clinician.