River and Green Noise for Focus
A centered noise bed and flowing water for sustained desk work.
- Green Noise 60%
- River 35%
Noise Colors Explained: White, Pink, Brown and More
Noise colors describe how a random signal’s power is distributed across frequencies. White noise has equal power per hertz, pink noise falls by 3 dB per octave, and brown noise falls by 6 dB per octave. That makes white sound bright, pink more balanced, and brown deep. The names describe spectra, not proven effects on sleep, focus, or health.
Noise colors comparison
| Noise color | Power change as frequency rises | Typical character | Practical use |
|---|---|---|---|
| White | 0 dB per octave per hertz | Bright, hissy, static-like | Broad masking, especially sharper sounds |
| Pink | −3 dB per octave | Balanced, soft rain or distant surf | Gentler broadband background |
| Brown / red | −6 dB per octave | Deep waterfall or low rumble | Low-frequency masking |
| Blue | +3 dB per octave | Crisp, bright hiss | High-frequency emphasis and audio testing |
| Violet / purple | +6 dB per octave | Very sharp, intense hiss | Specialized signal processing and testing |
| Grey | Shaped for roughly equal perceived loudness | Perceptually even, profile-dependent | Hearing and audio calibration contexts |
| Green | No single accepted technical definition | Usually mid-focused or nature-like | A listening label; check each generator |
The slope figures describe power spectral density. They do not mean every recording will sound equally loud. Speakers, headphones, playback level, frequency range, and hearing all change the result.
Why noise has colors
The analogy comes from light. White light combines visible wavelengths; white noise spreads power evenly across frequency when measured per hertz. Engineers then use other color names for different spectral slopes.
Human hearing does not treat frequency linearly. An octave from 100 to 200 Hz contains 100 one-hertz bins, while an octave from 5,000 to 10,000 Hz contains 5,000. White noise assigns equal power to each bin, so higher octaves contain much more total energy and sound bright. Pink noise reduces power as frequency rises, leaving roughly equal power in each octave. Brown noise reduces it more steeply.
The word “color” says nothing about the time pattern. Two pink-noise recordings can share an average spectrum while differing in peaks, loops, dynamics, and comfort.
White noise
White noise has constant power spectral density: equal power in equal-width frequency bands. It often resembles radio static, rushing air, or a strong fan.
Strength: broad high-frequency content can make speech edges, keyboard clicks, or small household changes less distinct.
Tradeoff: the bright hiss can become tiring, especially through headphones or at high levels.
Evidence boundary: continuous white noise has been studied for sleep and cognition, but results vary. A sleep systematic review rated the evidence very low quality. A 2024 meta-analysis found small task benefits in young people with ADHD or elevated attention problems and small average harms in comparison groups without those difficulties. White noise is not a universal cognitive aid or treatment.
Play white noise in the browser.
Pink noise
Pink noise follows an approximate 1/f power relationship. Power drops by 3 dB each octave as frequency rises, leaving roughly equal power per octave. It usually sounds softer and more natural than white noise.
Strength: broad coverage with less upper-frequency emphasis.
Tradeoff: it may not cover sharp high-frequency sounds as strongly as white noise at the same perceived level.
Evidence boundary: sleep laboratories have used short pink-noise pulses timed to measured slow waves. That closed-loop protocol differs from playing a continuous track. Ordinary pink noise should not be marketed as a way to increase deep sleep based on those experiments.
Play pink noise in the browser.
Brown noise, also called red noise
Brown noise follows an approximate 1/f² power relationship, falling by 6 dB per octave. “Brown” refers to Brownian motion, named after botanist Robert Brown, not to the color brown. “Red noise” is another name for the same downward spectral tendency.
Strength: its low-frequency weight can make traffic, HVAC, and distant rumbles less prominent.
Tradeoff: it provides less high-frequency masking, and small speakers may reproduce the bass unevenly.
Evidence boundary: brown noise is popular for sleep and concentration, but direct outcome research is sparse. Its most defensible use is as a comfortable masking option. Read the science and limits of brown noise.
Play brown noise in the browser.
Blue noise
Blue noise increases power by about 3 dB per octave, the spectral opposite of pink noise. It has more high-frequency energy and sounds brighter than white noise.
Common uses: audio testing, dithering, and applications that need less low-frequency energy.
Listening tradeoff: its brightness can become uncomfortable quickly. It is a poor default for long headphone sessions, sleep, or anyone sensitive to high frequencies.
Play blue noise in the browser.
Violet noise
Violet noise increases power by about 6 dB per octave, making it the spectral opposite of brown noise. It places still more energy toward the upper end of the chosen frequency range.
Common uses: specialized testing and signal processing.
Listening tradeoff: it can sound piercing. Keep levels restrained and stop if it causes discomfort. Claims that violet noise treats tinnitus or another condition require clinical context and should not be inferred from its spectrum.
Grey noise
Grey noise is shaped around an equal-loudness curve so frequencies are intended to sound similarly loud to a typical listener. There is no single universal grey-noise spectrum because equal-loudness contours depend on playback level and vary between people.
Common uses: perceptual audio testing and hearing-related calibration.
Listening tradeoff: a generic grey-noise track cannot be perfectly matched to your hearing, device, and level.
Play grey noise in the browser.
What about green noise?
“Green noise” has no widely accepted standard comparable with white, pink, or brown noise. Some generators use the label for a mid-frequency emphasis; others use it for filtered pink noise or nature-like sound. The name alone cannot tell you the spectrum.
Check the provider’s definition or simply judge the recording as a listening option. Do not assume that every green-noise track has the same acoustics or health effect.
Play Slo’s green-noise version or combine it with water in the River and Green Noise preset.
Which noise color should you choose?
Choose by the sound you need to soften and what your device reproduces comfortably.
| Situation | First choice | Reason to change |
|---|---|---|
| Voices and sharp room noise | White or pink | Switch if hiss becomes tiring |
| Low traffic or mechanical hum | Brown | Switch if bass feels uneven |
| General background for reading | Pink | Try silence if it adds distraction |
| Bright morning atmosphere | Blue at a low level | Avoid if high frequencies bother you |
| Audio or hearing test | The protocol’s specified color | Do not substitute based on preference |
| “Green noise” recommendation | Check the actual recording | The label is not standardized |
For sleep, focus, or study, spectrum is only one variable. Sudden peaks, audible loops, volume, speaker position, and preference can matter more. Our direct brown, white, and pink noise comparison helps with the three common options.
Listen safely
Use the lowest level that serves the masking purpose. A phone’s 50% setting is not 50 dB; output varies by device, headphones, distance, and recording. The World Health Organization advises adults to keep average personal-audio exposure below 80 dB and to reduce listening time as level increases. Background noise for sleep or work should not feel forceful.
Keep alarms, traffic, doorbells, and nearby people audible. Stop or lower playback if you notice ringing, muffled hearing, pain, or fatigue.
Noise-color presets
Hear a noise color inside a soundscape
Compare green noise with flowing water or use a low brown-noise base for focused work. Adjust each layer rather than raising the whole mix.
Deep Work Studio
A low noise floor, spacious focus ambience, and barely audible keys for a settled desk.
- Brown Noise 48%
- Deep Focus 32%
- Keyboard Typing 9%
Frequently asked questions
How many noise colors are there?
There is no fixed count. White, pink, brown or red, blue, violet, and grey have established technical uses. Other labels, including green, black, and orange, may vary between fields and generators.
What is the difference between white, pink, and brown noise?
White noise has equal power per hertz and sounds brightest. Pink noise falls by 3 dB per octave and sounds more balanced. Brown noise falls by 6 dB per octave and sounds deepest.
Which noise color is best for sleep?
No color has been proven best for everyone. Brown noise may suit low rumbles, pink noise offers softer broad coverage, and white noise can cover sharper sounds. The useful choice masks the actual disturbance at a low, comfortable level.
Which noise color is best for focus?
Brown or pink noise is a practical starting point because both avoid language and can feel less harsh than white noise. Research does not show a universal focus benefit. Compare the sound with silence on the same task.
Is green noise a real noise color?
It is a popular label but not a single standardized spectrum. Different generators may produce different signals under the name. Check or listen to the specific recording rather than relying on the label.
Research referenced
- Riedy and colleagues (2021), Noise as a sleep aid: A systematic review.
- Nigg and colleagues (2024), Do White Noise or Pink Noise Help With Task Performance in Youth With ADHD or Elevated Attention Problems?.
- Ngo and colleagues (2013), Auditory Closed-Loop Stimulation of the Sleep Slow Oscillation Enhances Memory.
- World Health Organization (2026), Deafness and hearing loss: Safe listening.
Related guides
- Brown Noise vs White Noise vs Pink Noise
- Best Sounds for Focus
- Best Sounds for Deep Sleep
- How to Use Sound Mixing
Want to compare more textures? Download Slo for a broader library of curated sounds and saved mixes on supported platforms.
Explore more sounds in Slo
Stack two or three sounds, keep the blend, and let the timer stop it. Slo, on iOS, Android and Mac.
