Brown noise for babies

What this sound is

In brown noise the power falls steeply as frequency rises, about 6 decibels per octave, twice the slope of pink noise. The highs are nearly erased, leaving a deep, rounded rumble you feel in the chest as much as hear. The name has nothing to do with colour: it refers to Brownian motion, named after the botanist Robert Brown, because the signal is mathematically a random walk. To the ear it is distant thunder, the cabin drone of an aircraft, or a large waterfall. The card in the app puts it plainly: the deepest, bassiest of the three. It plays as a constant rumble for as long as you need; small phone speakers cannot reproduce all of the bass, which is normal.

Why it may help

The womb was a low-frequency rumble largely free of high frequencies, and of the three noises brown comes closest to that description. For masking it covers low sounds best, traffic, neighbours, the hum of a building, and covers sharp sounds like a slammed door less well than white noise. On the evidence we should be plain: we know of no study that has looked at brown noise in babies specifically, and noise colour is thinly studied even in general. If the white noise evidence is weak and mixed, claiming more for brown would not be honest. Some babies prefer it, some do not; a few nights and a look at the log is the only way to find out.

Safe use

A bass-heavy sound pushes a small speaker and can lead you to raise the volume without noticing; the rule is the same and is laid out in the white noise guide.

• Keep the volume low: the level recommended for hospital nurseries is about 50 decibels. The practical test is simple: if you can talk in a normal voice in the room and still be heard easily, the level is fine; if the sound drowns you out, it is too loud.
• Do not put the phone or speaker in the cot or on its edge. Keep it at least one to two metres away, and avoid headphones, sound toys attached to the cot and any speaker close to the baby's ear.
• Use the timer. Fading the sound out 20 to 30 minutes after your baby has fallen asleep is usually enough. If you leave it on through the night, keep the level genuinely low.
• Turn it down once your baby has settled, and do not let a loud setting become the habit even briefly. Do not leave it running all day while your baby is awake, because it masks the speech they learn from.
• Phone speakers reproduce bass poorly, so do not turn it up because it feels faint; keep the level below normal speech.

How to play it in Agubu

1. Open Agubu, go to the Sounds tab at the bottom and tap the Brown noise card under Noise. This sound is in the free tier; there is no account to create and nothing to download, it plays on your device offline.
2. Set the volume with your own ears first: if you can speak in a normal voice in the room and still be heard, it is low enough. Place the phone one to two metres from the cot.
3. Tap Timer and pick a duration. When it runs out the sound does not stop abruptly; it fades down slowly. Twenty to thirty minutes after your baby has fallen asleep is enough on most nights.
4. If you like, layer it in the Mixer: brown noise with the womb sound makes a deep, familiar bed of sound. The Mixer is a Premium feature and blends up to four sounds at separate levels. Sounds play without ads and the app needs no internet connection.

When to use it

• When white or pink noise seems to unsettle your baby, as the deeper, softer option.
• In homes where low rumbles wake the baby: traffic, a lift, the neighbours.
• While rocking your baby to sleep; the deep tone pairs well with a slow rocking rhythm.