White, Pink and Brown Noise: What the Colours Mean

Three buttons on a noise generator, three names borrowed from light: white, pink and brown. It sounds like branding, but the names stand for a real difference in how each one spreads its energy from low pitches to high. That difference is why one sounds like static, one like rain and one like the inside of a plane. None of them is "just noise". Each has a specific shape, and that shape is what a speaker engineer, a sleep-app maker and a bored commuter are each after when they pick one over the others.

Equal energy per hertz, and why that isn't neutral

White noise has the same power at every frequency. Rational Acoustics' own guide to the three colours, written for engineers using its Smaart measurement software, defines it simply: white noise "contains equal energy across all frequencies" and has "equal power in each bandwidth". The slice from 1,000 to 1,001 Hz carries exactly as much power as the slice from 15,000 to 15,001 Hz. To an instrument that reads a fixed number of hertz at a time, that really is neutral. But our ears don't hear in fixed slices of hertz. We hear pitch in octaves, each one a doubling of frequency, and every octave up is twice as wide as the last. The octave from 1,250 to 2,500 Hz is 1,250 Hz wide; the octave from 10,000 to 20,000 Hz, three octaves higher, is 10,000 Hz wide, eight times as much. With equal energy per hertz, that top octave carries eight times the power of the one three octaves below. Your ears hear that as sound piled up at the top: thin and hissy, more like a radio between stations than anything that feels balanced.

Equal energy per octave: pink noise's −3 dB slope

Pink noise is designed to cancel out exactly that. Instead of keeping the power flat per hertz, its power drops as the pitch rises, at just the rate that gives every octave the same total energy. The same guide states it directly: pink noise "has equal energy per octave," produced by a spectrum whose "intensity level is reduced by 3 dB/octave." That −3 dB-per-octave tilt is the whole trick. It exactly cancels out each higher octave being twice as wide, so no octave dominates the way the top of white noise does. It's also why pink, not white, is the signal audio engineers reach for. The same source notes that pink noise "is used to measure the frequency response of a room or a system," while white noise, though sometimes used as "a reference tone for Transfer Function measurements," is described in the same guide as "not ideal" for that job on the octave-based charts audio measurement actually uses.

Brown noise: a steeper slope, and a name that isn't about colour

Brown noise, also called red noise, drops off faster still. Pink loses 3 dB per octave; brown loses twice that. An EBSCO Research Starters entry on Brownian noise gives it as "a −6dB/oct decrease in energy — or a power spectrum proportional to 1/frequency²." At that slope the bass takes over so completely that most of the energy above a few hundred hertz has all but disappeared, which is why brown noise sounds like a low rumble rather than a hiss. The name is a common trap. It sounds like a third colour next to white and pink, but the same EBSCO entry is clear that it isn't: brown noise "takes its name from Scottish botanist Robert Brown," whose 1827 observation of pollen jiggling randomly in water gave Brownian motion its name. The noise is called Brownian "because its signal changes follow a random-walk pattern," the same kind of randomness. A separate account on Wikipedia's Brownian noise entry confirms how it's made: brown noise "can be produced by integrating white noise", meaning you add up a white-noise signal over time, the way a random walk adds up its steps. So "brown" is a coincidence of English: the colour and the scientist's surname just happen to match. "Red", the other name, is the real colour comparison, because red light sits at the low end of the visible spectrum, the way brown noise's energy sits at the low end of what we hear.

What we measured

We measured how steeply each of the three colours from our noise generator tilts, using a simple roughness test: compare the energy in the signal with the energy in the difference between each sample and the one before. For completely random noise that comes out near 2.0, and it drops as the sound tilts toward the bass. White measured 2.008, almost exactly the 2.0 you'd expect. Pink measured 0.353, and brown 0.039. They fall in the order the −3 and −6 dB slopes predict, each roughly ten times apart. All three start at the same −20 dBFS level and stay matched whenever you switch between them, because each one is scaled to the same peak level before it plays, rather than played at whatever level its recipe happens to produce.

What each one is really for

Pick the colour for the job, not the mood. Pink is the standard for matching the volume of two speakers and for measuring how a room or system responds across the range, because its equal energy per octave matches both how we hear and how measurement charts are drawn. It's a steady sound that treats every octave the same, which a sweeping tone can't do. White is right when equal energy per hertz is really what you need, or as a quick check that something is producing sound across the whole range. It's a poor choice for testing a system on measurement charts, for the same reason it sounds thin rather than neutral. Brown and red swap precision for comfort. Their soft top end makes them the most pleasant to sit through for a long time, but that same soft top end makes them worse at revealing detail across the full range than a flatter sound.

Sleep, tinnitus and focus: what the evidence really shows

Search for any of these colours and you'll find plenty of claims about sleep, concentration and tinnitus relief. Most of that is thin, uncontrolled or written to sell something. There is one real data point for tinnitus. A small clinical study published in the American Journal of Translational Research followed 43 adults with tinnitus and hearing loss through pink-noise sound therapy delivered alongside their hearing aids, and found their Tinnitus Handicap Inventory scores dropped significantly at one, three and six months. It didn't compare pink noise with white noise or with no treatment, and the authors say so themselves, writing that the sample size "may have affected the generalizability of this work" and that "further neurophysiologic research and extensive clinical observation are needed before this becomes a routine treatment." That's a genuine result from one small trial, not proof that pink noise treats tinnitus, and neither this site nor its noise generator claims it does. If tinnitus is new, sudden or only in one ear, consult a specialist rather than opening a browser tab.

This page doesn't measure your room or your hearing. It explains what the three sounds are and what they were made for, not what your speakers or ears will do with them. If you want the same "per hertz versus per octave" idea applied to how digital audio is stored, sample rate and bit depth explained covers it, including how the faint hiss from rounding digital audio behaves like a very quiet cousin of white noise. When the room is what you're investigating rather than the sound, speaker placement and room acoustics explains what pink noise is actually revealing when it's used that way. And because noise carries far more total energy than a single tone at the same setting, how loud is too loud is worth a read before you leave any of the three running at a level you wouldn't choose for a tone.