White, pink and brown noise: what's the difference?
They are the same kind of sound, a steady hiss, with the energy tilted differently. White noise has equal energy at every frequency and sounds bright. Pink noise loses 3 decibels per octave and sounds even, like steady rain. Brown noise loses 6 decibels per octave and sounds deep, like a distant waterfall.
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The three colours
| Colour | Energy by frequency | Sounds like |
|---|---|---|
| White | Equal at every frequency | Radio static, a hissing radiator |
| Pink | Falls 3 dB per octave: equal energy in each octave | Steady rain, wind in leaves |
| Brown (also called red) | Falls 6 dB per octave | A waterfall heard from a distance, a low roar |
Because our ears are most sensitive to higher frequencies, white noise sounds harsher than its flat spectrum suggests. Pink noise matches the way hearing groups frequencies into octaves, which is why it sounds balanced. Brown noise is named after Robert Brown and Brownian motion, the random walk that produces its spectrum, not after the colour.
What noise is actually good for: masking
The well-established effect of steady noise is masking. A constant, featureless sound raises the level a sudden sound has to reach before you notice it, so a door, a voice or traffic stands out less. That part is basic acoustics.
Does noise improve sleep?
The evidence is weaker than the popularity of noise machines suggests. A 2021 systematic review of noise as a sleep aid judged the overall quality of evidence to be low and the findings inconsistent [1].
There is also newer evidence of a cost. A 2026 sleep-laboratory study reported by Penn Medicine found that pink noise played at 50 decibels through the night reduced REM sleep by about 19 minutes, and that earplugs did better at protecting sleep from intermittent noise [2].
A sensible reading: noise can help you fall asleep in a noisy place by covering sudden sounds. Playing it all night at a high level is not clearly good for you.
If you use it
- Keep it as quiet as still does the job.
- Use a timer so it fades out after you're asleep, rather than running all night.
- Pick the colour you find least intrusive. There is no good evidence that one colour is better for sleep or concentration than another.
The binaural app has a noise machine with a continuous dial from white through pink to brown, and a timer.
Questions people ask
- What is the difference between white, pink and brown noise?
- White noise has equal energy at every frequency. Pink noise falls by 3 decibels per octave, so each octave carries equal energy. Brown noise falls by 6 decibels per octave, so it is dominated by low frequencies.
- Which noise colour is best for sleep?
- There is no good evidence that one colour is better than another. A 2021 systematic review rated the evidence for noise as a sleep aid as low quality, and a 2026 sleep-lab study found pink noise at 50 decibels reduced REM sleep. If noise helps you fall asleep, keep it quiet and use a timer.
- Why is it called brown noise?
- It is named after the botanist Robert Brown. Its signal follows Brownian motion, a random walk, which produces a spectrum that falls 6 decibels per octave. It is also called red noise.
- Is brown noise good for focus or ADHD?
- Many people say they like working with it, and steady noise does mask distracting sounds. Evidence that brown noise specifically improves attention is limited, and it is not a treatment for ADHD.
- Is it safe to sleep with white noise all night?
- At low volume it is unlikely to harm hearing, but recent sleep-lab research suggests continuous noise through the night may reduce REM sleep. A timer that fades the sound out is a reasonable precaution.
Sources
- Riedy, S. M., Smith, M. G., Rocha, S., & Basner, M. (2021). Noise as a sleep aid: a systematic review. Sleep Medicine Reviews, 55, 101385. doi.org/10.1016/j.smrv.2020.101385
- Penn Medicine (2026). Pink noise reduces REM sleep and may harm sleep quality. News release on a sleep-laboratory study. pennmedicine.org