How to use it
Press Play, then pick a colour. Start with the volume low and raise it slowly: steady noise is tiring, so choose a level at which you could still hold a conversation. Press Play again or tap Space to stop. The graph shows the spectrum of what you hear, with frequency across the bottom on a logarithmic axis from 20 Hz to 20 kHz and level up the side in decibels. The dashed line is the slope the chosen colour should have in theory, and the “Measured live” readout fits a straight line to the live spectrum between 100 Hz and 8 kHz so you can compare the two.
Controls
- Colour: white, pink, brown, blue, violet or green. Keys 1 to 6 choose them.
- Volume: a master level. Colours are matched in loudness, so switching does not make a sudden jump.
- Low-cut and high-cut: two filters (20 Hz to 1 kHz and 1 kHz to 20 kHz) that trim the bass or the treble. Both are Off at their end stops.
- Stereo: on, the left and right ears get different noise; off, both get the same signal.
- Sleep timer: Off, 15, 30 or 60 minutes, with a countdown and a slow fade at the end.
- Reset restores every setting. The sound stops when you leave or close the page.
How it works
Noise is a random signal. You cannot predict the next sample, but you can describe how its power is spread over frequency. That description is the power spectral density: the power in a narrow slice of the spectrum, per hertz. A colour name is shorthand for the shape of that curve, borrowed from white light, which contains all visible frequencies. If the density follows a power law, it can be written as:
- White (n = 0, 0 dB/octave): equal power per hertz. Because each octave spans twice as many hertz as the one below it, the upper octaves hold most of the power and white noise sounds hissy. It is used for sound masking.
- Pink (n = 1, −3 dB/octave): equal power per octave. From f to 2f the power is the integral of C/f, which is C·ln 2 for every octave. Engineers use it to measure rooms and to set up loudspeaker systems, because an octave-band analyser shows it as flat.
- Brown or red (n = 2, −6 dB/octave): a random walk, the running sum of white noise. The name comes from Robert Brown and Brownian motion, not from the colour. It is a deep rumble.
- Blue (n = −1, +3 dB/octave) and violet (n = −2, +6 dB/octave): the mirror images, with power rising toward the treble. Violet is white noise differentiated. Blue-type noise is used in dithering, where it hides rounding error at frequencies where it is less noticeable.
- Green is not a standard colour. Here it is white noise confined to a bell-shaped band centred on 500 Hz, with most of its power between about 250 Hz and 1 kHz.
The page builds each colour once, when you first select it. It fills a spectrum with random complex numbers, scales their size by the power law and applies an inverse fast Fourier transform. The result is 11.9 seconds of noise (219 samples at 44.1 kHz) that repeats seamlessly, because the signal is periodic by construction. The left and right channels are independent. Frequencies below 20 Hz are rolled off so brown noise does not waste energy on inaudible rumble. Levels are matched by overall (RMS) power within 2.5 dB, but a hissy colour still sounds louder than a rumbly one, since the ear is most sensitive between 2 and 5 kHz.
Things to try
- Switch between white and pink and watch the dashed line tilt from flat to −3 dB per octave.
- Play brown noise, then turn the low-cut up to about 300 Hz. Most of what you heard as rumble disappears.
- Play violet with the high-cut at 3 kHz and compare it with pink.
- Turn Stereo off and listen on headphones: the noise moves from around your head to the middle of it.
- Set the 15-minute timer, press Play and watch the countdown. The final 30 seconds fade out.
Frequently asked questions
Does noise help you sleep or concentrate?
The research is mixed. Some studies find small benefits for some people, others find none, and evidence for any single colour is thin. This page is a demonstration, not medical advice. If you struggle to sleep or have hearing problems, talk to a health professional.
How loud should I play it?
Moderate. Loud sound played for hours can damage hearing, and you should still be able to hear alarms and people speaking to you.
Why does brown noise make my speakers rattle?
Its power is concentrated in the bass. Small speakers may distort, so lower the volume or raise the low-cut.
Is the noise really random?
It uses the browser’s pseudo-random number generator, which is fine for listening. The 11.9-second loop does repeat, though, and a very attentive listener may notice it.
Does it keep playing when I switch tabs?
On a desktop computer, yes: the noise continues in a background tab, and only the graph stops redrawing. The sleep timer still ends on time. Phones and tablets may pause web audio when the screen locks or the browser goes to the background, and the page cannot prevent that.