Brown noise is a steady hiss whose power falls by about 6 dB with every octave you go up in pitch. Because most of the energy sits in the low frequencies, it sounds deeper and softer than white noise or pink noise. This page explains where the name comes from, what the number means, and what researchers have and have not found.
What is brown noise?
Brown noise is a random signal with a lot of energy in the bass and very little in the treble. It is also called red noise or Brownian noise, and all three names describe the same sound.
The name does not refer to the colour brown. It honours Robert Brown, the botanist who documented the erratic motion of particles in water, now called Brownian motion. Brown noise is what you get when you add up random steps, the way a particle wanders. In signal terms, it is white noise that has been integrated, and its power is proportional to 1 divided by the frequency squared.
Digital brown noise is made the same way. Each sample is the previous one plus a small random offset, and many implementations add a slight decay so the signal does not drift away without limit. That running total is why the sound has such a heavy low end: slow changes pile up, while fast ones average out.
"Red" comes from an analogy with light. White noise is flat, like white light, and brown noise leans toward the low end of the spectrum, like the red end of the visible one.
Why does brown noise sound deeper?
Brown noise sounds deeper because it puts most of its energy into low pitches and much less into high ones. Your ear hears the balance, so the sound reads as heavy and dark.
The balance is steep. Every time the frequency doubles, brown noise loses about 6 dB of power, which means roughly a quarter of the power. Go up three octaves and the power is about 1/64 of what it was. White noise, by contrast, has the same power at every frequency, so the high end stays loud and the sound reads as a bright hiss.
People describe brown noise in everyday terms: a low roar like a waterfall, heavy rainfall or distant thunder. The Sleep Foundation reports that research participants compared it to rainfall or a shower. The soft, damped feel comes from the missing treble. There is still some high-frequency energy in brown noise, just far less of it.
What do the numbers mean?
The slope in dB per octave is the difference between the noise colours. A steeper downward slope means a deeper sound. Colours of noise are named by that slope:
| Colour | Slope | How it sounds |
|---|---|---|
| White | flat | Bright, even hiss |
| Pink | −3 dB per octave | Softer, like steady rain |
| Brown | −6 dB per octave | Deep, like a waterfall or distant thunder |
| Violet | +6 dB per octave | Thin and high, the opposite of brown |
The Sleep Foundation notes that pink noise drops about 3 dB per octave and sounds lower in pitch than white. It adds that brown noise falls off about twice as steeply as pink, so it sounds deeper than both. For a side by side look at all three, read white, pink and brown noise compared, or browse the rest of the noise colours section.
An octave is a doubling of frequency. The step from 100 Hz to 200 Hz is one octave, and so is the step from 1,000 Hz to 2,000 Hz. Because pitch is heard in octaves, a slope measured per octave matches how the sound feels to a listener: each step up gets a little quieter, and the steps add up.
One caution: "6 dB" is a ratio, not a loudness setting. It describes the shape of the sound, whatever the volume.
What does the research show?
Not much has been tested for brown noise itself. The Sleep Foundation says that the effect of brown noise on sleep has not been widely studied.
One recent laboratory study looked at whether the colours differ in how alert they make people. Researchers played white, pink and brown noise for 10 seconds each and tracked pupil size, a marker of arousal. They recruited 38 people and analysed data from 31. They found no significant difference in pupil size across the three colours, and concluded that popular claims about arousing or calming effects were not supported for listeners new to the sounds.
That study measured pupils. It didn't measure sleep, focus or mood, so it doesn't settle those questions either way. It does suggest that the choice between colours is largely about what you like to hear.
How can you try it?
The simplest way is to listen to white, pink and brown noise at the same low volume, one after another, and notice where the sound sits. Keep the volume comfortable. Brown noise can feel quiet because the low end is less piercing. That makes it tempting to turn up, so set the level first and leave it.
Hush Machine makes its noise live on your phone, so nothing loops or repeats, and one dial moves from white through pink and brown to deep brown. You can hear the slope change as you turn it. The brown noise page shows how that colour is built. Hush Machine is by Kallos Labs and is coming to iPhone.
Bottom line
Brown noise falls about 6 dB per octave, twice the slope of pink noise, so its energy sits in the low end and it sounds deeper. The evidence on what it does for sleep or focus is thin, so choose it by ear, as a sound you like.
Questions
- Is brown noise the same as red noise?
- Yes. Brown noise is also called red noise or Brownian noise. The name comes from Brownian motion, the random movement of particles, and not from the colour brown.
- Is brown noise deeper than pink noise?
- Yes. Pink noise falls about 3 dB per octave and brown noise about 6 dB per octave, so brown noise puts even more of its energy in the low end and sounds deeper.
- Does brown noise help you sleep?
- The Sleep Foundation says the effect of brown noise on sleep has not been widely studied. Some people use it to cover room noise, so try it at a comfortable volume and see how you feel.
- Is brown noise just a low rumble?
- No. It has energy in every octave, including the high ones. The high end is just much quieter than the low end, which is what gives it a soft, damped sound.