White noise for babies: distance, volume and the timer
Slo plays white noise for babies free in a browser tab at slonoise.com, and on iPhone, Android and Mac, with a timer you set and one fader you can leave low. The setting that matters most is not on the screen: put the speaker across the room rather than on the cot rail, because a 2014 Pediatrics study measured every infant sleep machine it tested above the nursery noise limit at 30 cm.
What the measured numbers say
Sarah Hugh and colleagues at the University of Toronto bought 14 infant sleep machines, played each at maximum volume, and measured the sound pressure at 30, 100 and 200 cm, correcting for the size of a six-month-old’s ear canal. Thirty centimetres is roughly a cot rail. Two hundred is roughly across the room.
Two numbers came out of it. At 30 cm, all 14 machines exceeded 50 A-weighted dB, which is the noise limit currently recommended for infants in hospital nurseries. Three of them exceeded 85 dBA, a level that breaches adult occupational exposure limits if it runs for more than eight hours.
The authors’ own advice follows from that: keep the machine as far from the infant as you can, never in the cot or on the rail, at the lowest volume and for the shortest time. Sound pressure falls fast with distance, so moving the speaker two metres away is a larger change than anything you can do with a fader. Set the distance first and the level second.
What a background sound does not do
It does not soundproof a room. A steady sound raises the noise floor so that sudden sounds stand out less against it, which is a different thing from stopping them arriving. Where you can quiet the source instead, the World Health Organization’s noise guidance says that is the better move.
The research is also thinner than the product category suggests. The 2021 systematic review of white noise and sleep in Sleep Medicine Reviews rated the evidence very low quality with mixed results, so nobody can honestly tell you what a track will do for one child.
And it answers none of the real questions. A baby who is hungry, unwell, too warm or working through a developmental change is not a volume problem. If sleep is a persistent worry, that belongs with a paediatrician. This page carries no age guidance for starting or stopping, and no recommendation about your child, because nobody can give either one at a distance.
Reading the fader
A fader is a scale on the audio signal, not a decibel reading. Three things the app cannot see decide what reaches the cot: how high the device volume sits, how efficient its speaker is, and how far away it stands. The same 40% on a phone on a chest of drawers and on a Bluetooth speaker on the floor are two different rooms.
So set it by ear, in the right place. Start the sound, walk to the cot, and turn it down until it is quieter than feels right from the doorway. A workable check: someone speaking normally at the door should still be clearly audible over it. If you want a number rather than an impression, a phone sound-level app will read the level at cot height, and it is worth doing once.
Our own nursery preset opens at 40% with an all-night timer already set, and states the same distance point on the page. Forty per cent is a starting position, not a safe level. There is no such thing as a safe fader position, only a safe level in a room.
Choosing a timer length
The timer is the duration control the study’s advice asks for, and it is the one most people never touch.
A short timer of 30 to 60 minutes covers the settling period and then leaves the room quiet. An all-night timer keeps the noise floor steady, so a bin lorry at five in the morning arrives against a background rather than into silence. The trade is plain: the second option runs the sound for eight hours, which is the opposite of the shortest-duration advice.
We ship the all-night preset because that is what people look for. It is also the version where distance and level stop being fine detail and start being the whole thing.
White, pink and brown in a nursery
The three differ by how energy is spread across the spectrum. That is a description of the sound, not a ranking.
| Colour | Slope | What it sounds like |
|---|---|---|
| White | Flat per hertz | A bright, even hiss, with plenty of treble |
| Pink | −3 dB per octave | Softer and rounder, closer to steady rain |
| Brown | −6 dB per octave | A low rumble, most of its energy at the bottom |
Two practical notes. A small speaker reproduces very little below about 200 Hz, so brown noise from a phone is mostly the part of brown noise that is missing. And low frequencies pass through walls more readily than high ones, so a brown-noise floor in one room is more audible in the next room than a white-noise floor at the same setting.
If a flat tone bothers you, rain layered under soft pink noise gives the same steady floor with some texture in it. The colours of noise page sets out the slopes in more detail.
When to stop white noise
There’s no medical age to aim for. The 2014 study above measured sound pressure from infant sleep machines; it never tested when to retire one. The AAP’s 2023 noise statement advises placing sleep machines away from the child, keeping volume low and limiting use, but it gives no age to stop. Treat any exact age you read elsewhere as a guess, not a finding.
In practice, a toddler is ready to try without it once the sound has become background rather than a requirement, when a nap without it goes about the same as a nap with it. Weaning works better as a fade than a cutoff.
Reverse the level and timer, over a week or two. First, lower the level a notch every few nights until it is barely audible. Once it is low, switch an all-night timer to one that ends twenty or thirty minutes after your toddler is usually asleep, so the room goes quiet after the hard part is done rather than at random. Then stop playing it. If a night goes badly, hold that step for a few more nights rather than starting over.
Leave everything else in the routine untouched: same bedtime, same book, same room. The sound was one layer in the routine, not the routine itself, and one layer comes out more cleanly when nothing else changes with it.
Two things are specific to this age. Many daycare rooms don’t run a sound machine, so it is worth testing a nap without one before your toddler needs it to work away from home. Travel cuts the other way: bring the same device and the same setting, because a hotel room without the familiar sound can make that night harder. And if your toddler asks for the noise by name, that is usually a request for the routine around it, not evidence that the sound itself is doing anything. A song or a few minutes of talking often covers the same ground.
If you keep it running past this point, the distance and volume guidance above still applies. A toddler bed sits differently in the room than a cot did, so it is worth rechecking where the speaker sits rather than assuming last year’s spot is still the right one.
Nothing to install
The player runs in a browser tab. Open the page, pick a sound, set a timer, set a level. No download, no account, no machine to buy, and no app quietly holding the screen awake on the phone you also use as a monitor. The Slo mixer runs the same way if you want two layers instead of one, and there are downloads for iPhone, Android and Mac when you want the sounds without a tab open.
Common questions
Is white noise safe for a baby?
The measured part has an answer. A 2014 Pediatrics study played 14 infant sleep machines at maximum volume and recorded every one of them above 50 A-weighted dB at 30 cm, the limit recommended for hospital nurseries, with three above 85 dBA. Its authors recommend keeping the machine as far from the infant as possible, never in the cot or on the rail, at the lowest volume and for the shortest time. What is right for your child is a question for your paediatrician, not for a website.
Can I leave white noise on all night?
Both practices are common, and the study above points the other way: its authors recommend the shortest duration you can manage. A timer is the control that lets you decide instead of defaulting. If you do run it all night, the distance and the level are the two things worth tightening.
White noise or pink noise in a nursery?
They differ in spectrum, not in kind. White noise carries equal energy per hertz, so it sounds like a bright hiss. Pink noise falls by 3 dB per octave, so it sounds softer and rounder. Neither is the correct one; pick whichever you can run at a lower level and still not notice.
Do I need a white noise machine?
No. A machine is a speaker with a dial in a plastic case. The same noise plays in a browser tab with a timer and a volume slider, and a slider you can read beats a dial you cannot.
When should I stop using white noise for a toddler?
There’s no medical age to stop at. The 2014 study above measured sound pressure, not when to retire a machine. The AAP’s 2023 noise statement advises placing sleep machines away from the child, keeping volume low and limiting use, but gives no age to stop. In practice, wean over a week or two: lower the volume a notch every few nights, then shorten an all-night timer to end after your toddler is usually asleep, then drop it. Keep the rest of the bedtime routine the same, and expect naps away from home, at daycare or on a trip, to work differently than the machine at home.
Sources
- Hugh SC, Wolter NE, Propst EJ, Gordon KA, Cushing SL, Papsin BC (2014). Infant sleep machines and hazardous sound pressure levels, Pediatrics 133(4), 677-681. Abstract on PubMed. Carries the 14 machines, the 30/100/200 cm distances, the 50 dBA and 85 dBA figures, and the placement advice.
- Balk SJ, Bochner RE, Ramdhanie MA, Reilly BK; AAP Council on Environmental Health and Climate Change, Section on Otolaryngology–Head and Neck Surgery (2023). Preventing Excessive Noise Exposure in Infants, Children, and Adolescents, Pediatrics 152(5), e2023063752. On sleep machines, advises locating them as far from the infant as possible, keeping the volume as low as possible, and limiting use, without giving an age at which to stop.
- Riedy SM, Smith MG, Rocha S, Basner M (2021). Systematic review of the effects of white noise on sleep, Sleep Medicine Reviews 55, 101385. Carries the point that the evidence is very low quality and mixed.
- World Health Organization (2018). Environmental Noise Guidelines for the European Region. Carries the point that reducing the source beats covering it.
Related reading
- The colours of noise explains what the spectral slopes mean.
- How sound affects sleep quality covers what a raised noise floor does and does not change.
Explore more sounds in Slo
Stack two or three sounds, keep the blend, and let the timer stop it. Slo, on iOS, Android and Mac.
