For helping babies fall asleep, white noise has the stronger research behind it, but brown noise can work just as well in practice. The key difference isn’t which color you pick. It’s how loud you play it and how long you leave it on. Both carry real risks to infant hearing and development if used incorrectly.
What White and Brown Noise Actually Sound Like
White noise combines every frequency the human ear can detect (20 Hz to 20,000 Hz) at equal volume. That equal distribution across high and low frequencies gives it a bright, hissing quality, like TV static or a running shower. Brown noise shifts the power toward lower frequencies, producing a deeper, richer rumble, more like a strong wind or a distant waterfall. Because brown noise lacks the higher-pitched hiss, many people find it softer and more pleasant to listen to.
Which One Has Been Studied in Babies
White noise is the only type that has been directly tested in infant sleep research. In a randomized trial of 40 newborns between 2 and 7 days old, 80% of the babies exposed to white noise fell asleep within five minutes, compared to just 25% who fell asleep on their own without it. That’s a striking difference, and it’s the number most pediatric sleep consultants point to when recommending sound machines.
Brown noise has not been tested in comparable infant studies. That doesn’t mean it’s ineffective. It simply means the evidence base doesn’t exist yet. Many parents report that their baby responds better to the lower-pitched rumble of brown noise, and that’s a perfectly reasonable observation. Babies are individuals, and some are more settled by deeper tones. The underlying principle is the same for both: a steady, continuous sound masks sudden noises (a door closing, a dog barking, a sibling yelling) that would otherwise wake a sleeping baby.
Why the “Womb Sound” Argument Favors Lower Frequencies
One reason brown noise appeals to parents is that the sound environment inside the womb is predominantly low-frequency. Blood flow, the mother’s heartbeat, and muffled external sounds create a constant, deep hum that newborns have been listening to for months. Brown noise mimics that tonal profile more closely than white noise does. Some parents find their baby calms faster with it, especially in the first few months of life when the transition from womb to world is still fresh. White noise works through the same masking mechanism but includes higher frequencies that the baby wouldn’t have heard much of in utero.
Volume Matters More Than Color
The real danger with any sound machine isn’t which type of noise it plays. It’s how loud it gets. Research has found that many commercially available white noise machines can exceed 91 decibels on their maximum setting, which is louder than what occupational safety guidelines consider safe for a two-hour adult work shift. Smartphone apps are potentially even worse, since their output is limited only by the phone’s speaker hardware, which can reach around 100 decibels. That’s roughly the volume of a power tool.
Babies sleep 10 or more hours a night, and many also nap with a sound machine running. That extended exposure magnifies the risk. Animal studies show that continuous moderate-intensity noise exposure during early development damages both auditory processing and cognitive development. A scoping review published in Sleep Medicine concluded that white noise machines “may lead to poor hearing, speech, and learning outcomes if used incorrectly.” The concern applies equally to brown noise or any other continuous sound played too loudly or for too long.
As a general guideline, 70 decibels (about the volume of a dishwasher running in the next room) is considered safe for any duration. Above that threshold, the longer the exposure, the greater the risk of hearing damage. Most sound machines don’t display their decibel output, so a practical test from the AAP is useful: if you have to raise your voice to talk to someone standing an arm’s length away from the machine, it’s too loud.
Safe Setup for Any Sound Machine
Placement matters as much as volume. The AAP recommends positioning a sound machine at least 7 feet from your baby’s head. That distance alone significantly reduces the decibel level reaching your baby’s ears, since sound intensity drops quickly with distance. Placing the machine on a dresser across the room rather than on the crib rail or a nearby nightstand makes a meaningful difference.
Beyond placement, a few other practices reduce risk:
- Use the lowest effective volume. Start quiet and increase only until it’s just loud enough to mask household sounds. You don’t need to drown everything out.
- Avoid running it all night. Using a timer to shut the machine off after your baby falls asleep limits total exposure. Many machines have 30, 45, or 60-minute auto-off settings.
- Skip phone apps when possible. A dedicated sound machine with a volume cap is safer than a phone speaker, which can output dangerously high levels.
- Keep it consistent. Whichever sound your baby responds to, stick with it. The familiarity becomes a sleep cue over time.
Choosing Between the Two
If your baby is a newborn and you want to go with what’s been formally studied, white noise is the evidence-backed choice. If your baby seems unsettled by the higher-pitched hiss of white noise, or if you simply prefer a deeper, softer tone, brown noise is a reasonable alternative that works through the same sound-masking principle. Some parents try both and let the baby’s response decide.
The color of the noise is far less important than getting the volume and placement right. A perfectly chosen sound played too loud or placed too close to the crib poses a genuine developmental risk. A modest, well-placed machine playing either white or brown noise at a low volume is one of the most effective, low-cost sleep tools available to new parents.