What noise colours actually are

Slope, not magic

Random noise contains every audible frequency at once. What differs between the colours is how energy is distributed across those frequencies. White noise holds equal energy in every hertz, which puts most of its power in the top octaves simply because the top octaves are wider - that is why it sounds bright and hissy. Pink noise sheds roughly 3 dB per octave, giving approximately equal energy per octave, which most listeners describe as balanced. Brown noise sheds about 6 dB per octave and ends up dominated by low frequencies, closer to a waterfall or heavy rain.

Why masking works at all

Masking is a property of hearing, not of the noise: a sound is harder to detect when another sound occupies the same frequency region at a similar or higher level. That is why the useful question is never "which colour is best" but "what am I trying to cover". Traffic rumble sits low; speech sits in the middle; a squeaking hinge sits high. Choose a spectrum that overlaps the intrusion, then use the lowest level that does the job.

What the labels do not tell you

The colour name says nothing about how a particular generator was filtered, how loud it is, or how your speakers reproduce it. Small laptop speakers roll off bass heavily, so brown noise through them can sound thinner than pink noise through headphones. Compare on the system you will actually use.

Claims that a specific colour treats a condition, repairs attention, or produces a guaranteed physiological change go well beyond the evidence. Steady background sound is a listening preference that many people find helpful; that is a reasonable claim, and it is where we stop.

Common questions

What is the difference between white, pink and brown noise?

They are the same random signal with different spectral slopes. White noise has equal energy per hertz, pink noise falls about 3 dB per octave, and brown noise falls about 6 dB per octave, which makes it sound progressively lower and softer.

Does brown noise block out noisy neighbours?

Masking raises the background level so intruding sounds stand out less. It does not cancel them. Low-frequency rumble through a wall is partly masked by brown noise, while speech is better covered by a broader spectrum.

Is one noise colour better for sleep or concentration?

There is no strong evidence that one colour is universally better. Preference varies between people, and comfort at a low listening level matters more than the label on the sound.