What is blue noise?
Blue noise, sometimes called azure noise, has power that increases by 3 decibels per octave. Where pink noise leans toward the bass, blue noise leans toward the treble. Mathematically, its power is proportional to frequency, the mirror image of pink noise’s 1/f.
The sound is sharp and thin, like a hissing kettle, spray from a hose or the sizzle of frying heard up close. Most people find it too bright for sleep on its own, but it is useful in particular situations.
What blue noise is used for
- Masking high-pitched sounds: whining electronics, ringing, squeaks and some kinds of tinnitus. Because its energy sits up high, it covers those sounds at a lower overall volume than white noise.
- Audio dithering: blue-weighted noise is used when reducing the bit depth of audio, because it pushes the added noise into frequencies where it is least audible.
- Graphics: in images and printing, blue noise patterns spread dots evenly without visible clumps, which is why it appears in computer graphics, halftoning and modern game rendering.
- Nature: the distribution of light-sensitive cells in the retina follows a blue-noise-like pattern, which helps avoid visual artifacts.
Blue noise vs violet and white noise
| Color | Slope | Sound |
|---|---|---|
| White | Flat | Bright hiss |
| Blue | Rises 3 dB per octave | Brighter, airy hiss |
| Violet | Rises 6 dB per octave | Very sharp, thin hiss |
If blue noise is too sharp, try mixing it with pink or brown noise using the sliders, or drag Tone toward Darker. For tinnitus specifically, the tinnitus sound therapy page has better tools.
Listen at a low volume
High frequencies are what the ear is most sensitive to, and what loud sound damages first. Blue noise can feel uncomfortable at volumes that would be fine with brown noise. Start low and raise it only until the sound you want to cover disappears.
Frequently asked questions
Is blue noise good for sleep?
On its own most people find it too bright for sleep. It can help if the sounds keeping you awake are high-pitched, and a little blue noise mixed under pink or brown noise adds clarity.
What is the difference between blue noise and violet noise?
Both get louder toward the treble. Blue noise rises 3 dB per octave and violet noise 6 dB per octave, so violet is sharper still.
Why is blue noise used in images?
Blue noise patterns have no low-frequency clumping, so dots or samples look evenly spread. That makes dithered images and rendered graphics look smoother.