White, pink and brown noise differ in one thing: how quickly the power falls as the pitch rises. White noise stays flat, pink falls 3 dB per octave and brown falls 6 dB per octave. The steeper the fall, the less hiss and the more low rumble you hear. This is the starting question for all the noise colours, so we begin with the numbers and then move on to how each one sounds.
What is the difference between white, pink and brown noise?
The difference is the slope of the spectrum. White noise has a flat spectrum, pink noise falls about 3 dB per octave and brown noise falls about 6 dB per octave, which is 20 dB per decade.
| Colour | Slope | What it sounds like |
|---|---|---|
| White | Flat (0 dB per octave) | Bright, steady hiss |
| Pink | −3 dB per octave | Softer, like steady rain |
| Brown | −6 dB per octave | Deep rumble, like a waterfall |
An octave is a doubling of frequency. Going up from 100 Hz to 200 Hz is one octave, and so is 1,000 Hz to 2,000 Hz. A slope of −3 dB per octave means each step up is a little quieter than the one before. A slope of −6 dB per octave means each step up drops twice as far, which is why brown noise sounds so much heavier at the bottom.
How does each one sound?
White noise sounds bright because it is flat. Each octave up holds twice as many frequencies as the one below, so the high end carries most of the total energy. You hear that as an even hiss, like static from an untuned radio. Our page on white noise has the longer version.
Pink noise sounds softer because the extra energy at the top is taken away. In pink noise every octave carries the same energy, so the low and middle range come forward. Most people describe it as steady rain. See pink noise for more.
Brown noise sounds deepest. It falls twice as fast as pink, so low frequencies dominate and the sound is a rumble, closer to a waterfall or a distant engine. The name comes from Brownian motion, the random movement it is modelled on, not from the colour. It is also called red noise. Hear it on the brown noise page.
Why does the same noise sound so different?
Your ear does not hear every frequency equally, and it hears pitch in octaves, not in equal steps of hertz. That is why a flat spectrum sounds bright. White noise gives the high octaves far more total energy than the low ones, because each higher octave spans more frequencies. Pink noise evens that out, so each octave gets the same energy, and the ear hears something balanced. Brown noise tilts past balanced, so the low octaves get the most energy and the top end fades away.
You can test this with one sound. Take a steady hiss and turn the treble down slowly. It passes through something like rain and ends at something like distant surf. Those are the same three colours, seen as points on one dial.
When do people pick each one?
People choose by taste and by what they want to cover. Some pick white noise to cover speech or street sounds, because its hiss reaches high into the range of voices. Some find it too sharp and move to pink. Others like brown for its low, even rumble, for example when working in a noisy room. These are habits people report, not results we can promise, and the studies above do not rank the colours. If one feels harsh after ten minutes, move one step down the dial.
What do studies say about the colours?
Not much, and what exists is mixed. The Sleep Foundation says evidence on white noise and sleep is mixed, reviewers question its quality, and the effect of brown noise on sleep has not been widely studied.
Two small studies looked at pink noise overnight:
- A cross-over pilot with 12 healthy adults played continuous pink noise at 45 dB for five nights. Pink noise alone did not significantly change sleep compared with quiet. It did reduce the sleep fragmentation caused by traffic noise. The authors call it an explorative pilot with a small, similar group of people.
- A study of 72 people played pink noise at 55 dB overnight, about two feet from the bed, and measured insight the next day. There was no significant difference between the groups. The authors suggest that constant pink noise may be detrimental to insight and creativity, and note they had few cases to go on.
Neither is a reason to pick one colour or avoid another. They show how little is settled, so be careful with any claim that one colour is best.
How loud should it be?
Keep it quiet. The Sleep Foundation notes there are no official volume guidelines for sleep sound machines, and suggests a level near a background conversation or light rustling, with the machine placed across the room.
For a sense of scale, NIOSH sets its recommended workplace limit at 85 dBA over eight hours, with every 3 dB increase halving the time. That is a limit for work, not a target for a bedroom, and we don't give a safe level of our own. Lower is better, and a timer helps.
Try it
Play each colour for a minute at the same low volume and compare. Notice how much of the hiss disappears from white to pink, and how much of the rumble arrives from pink to brown. Hush Machine, coming to iPhone, makes its noise live on the phone, so nothing loops or repeats. One dial runs from white through pink and brown to deep brown, and a timer and fade end the sound when you want.
Bottom line
It is the same kind of noise with a different tilt. White is flat and bright, pink is softer and brown is deepest. Pick the one that sounds comfortable to you, and keep it low.
Questions
- Is pink noise the same as white noise?
- No. White noise is flat, with equal power at every frequency. Pink noise falls about 3 dB per octave, so it has less high-frequency hiss and sounds softer.
- Why is brown noise called brown?
- The name comes from Brownian motion, the random movement the noise is modelled on, not from the colour. It is also called red noise.
- Which colour sounds deepest?
- Brown noise. It falls about 6 dB per octave, twice as fast as pink, so low frequencies dominate and it sounds like a deep rumble.
- Does one colour work better for sleep?
- Published research is limited and mixed, and brown noise has not been widely studied for sleep. Try each at a low volume and keep the one that feels comfortable to you.