Walk into any baby aisle and you will see white noise machines, pink noise machines, ocean-sound clocks, and a hundred different lullaby speakers. The marketing implies they all do roughly the same thing. They do not. The differences matter, both for whether the sound actually helps your baby sleep and for whether it is doing any of the things parents worry about — affecting hearing, affecting language development, becoming a sleep crutch.
This article walks through the three main categories — white noise, pink noise, and lullabies — and what the evidence says about each.
Muna was built around lullabies and gentle visuals because the science of how music engages the infant brain is different from, and complementary to, the science of ambient sound — and the two do different jobs.
What These Sounds Actually Are
White noise contains every audible frequency at equal intensity. The result sounds harsh — closer to television static than to anything in nature. It works as a sleep aid by masking sudden changes in environmental sound: a slamming door, a sibling's laugh, a car horn. The infant brain is wired to wake at sudden sound changes, and white noise blunts those changes by raising the floor of constant sound.
Pink noise also contains every frequency, but with the higher frequencies progressively quieter — which matches the way most natural sounds are distributed. Wind through trees, falling rain, a flowing river: all roughly pink. To the human ear pink noise sounds softer, deeper, and less hissy than white noise. It does the same masking job but feels less aggressive.
Brown noise (sometimes called red noise) takes the same idea further, with even more emphasis on low frequencies. It sounds like a distant waterfall or a low rumble. Some babies prefer it, particularly older infants.
Lullabies are something else entirely. They are music — pitched, rhythmic, emotional, often sung in a parent's voice or in voices that imitate parent-directed singing. Lullabies do not primarily mask environmental sound (their volume varies; they have melody and pauses). They engage attachment, emotional regulation, and the auditory-language system in a way ambient noise cannot. They are designed for connection, not masking.
These categories do different jobs. Treating them as interchangeable — looking only at "sleep sounds" — misses the point.
The AAP Volume Guidance and Why It Matters
In 2014, Hugh and colleagues published a study in Pediatrics called "Infant Sleep Machines and Hazardous Sound Pressure Levels." They tested fourteen popular infant sound machines at maximum volume and at a distance of 30 cm — a typical placement next to a cot. All fourteen exceeded 50 dBA, and three exceeded 85 dBA, the level at which prolonged exposure can damage adult hearing.
The American Academy of Pediatrics has since recommended:
- Volume at or below 50 dBA measured where the baby is (not at the speaker).
- Source at least 2 metres from the baby, ideally further.
- Not running the sound machine all night if a quieter setting and shorter use will achieve the same result.
A free smartphone decibel meter app, held at the cot, is enough to check volume. The number matters because the infant ear is still developing — the cochlea continues to mature into the toddler years — and prolonged exposure to elevated sound can affect frequency discrimination. The risk in real-world use is small for parents who pay attention to volume; the risk in real-world use is meaningful for parents who do not, because most machines are loud enough to do harm at maximum.
The 50 dB threshold is roughly the volume of a quiet conversation in a library. If you can speak normally over the sound and still hear yourself comfortably, you are probably in range. If the sound dominates the room, it is too loud.
White Noise and Pink Noise: When and How
The case for white or pink noise as a sleep aid in babies has reasonable evidence behind it. A 1990 study by Spencer and colleagues in the Archives of Disease in Childhood found that 80% of newborns fell asleep within five minutes when exposed to continuous white noise, compared to 25% in the control group. More recent work has replicated the effect at much smaller magnitudes — closer to a 10–20 minute reduction in sleep onset, which is still meaningful for an exhausted parent.
The case for using these specifically as masking — to cover household noise that wakes the baby — is stronger than the case for using them as a sleep aid in their own right. A baby who sleeps fine in silence does not need ambient noise; a baby who wakes at every passing footstep often does.
A few points that parents commonly miss:
- Pink noise is usually a better starting point than white noise. Same masking effect, gentler perceived sound, easier to keep at the lower end of the volume range.
- Don't increase volume to match a louder fuss. When the baby is fussing, the temptation is to turn the noise up. This is the wrong direction. The point of masking is steady, low-level sound — not a sound that competes with the cry.
- The 4S/5S approach uses noise as part of soothing, not as a permanent aid. Harvey Karp's "5 S's" use a loud "shhhh" sound to imitate the in-utero soundscape during active soothing of a young baby. That is a different use case from leaving a sound machine running through every nap; both can be reasonable, but they are not the same.
- Consider weaning around 12 months. Most infant sleep specialists suggest reducing reliance on continuous sound around the first birthday. The baby no longer needs the masking against household noise as protectively, and prolonged use beyond toddlerhood can build a stronger sleep dependency than is helpful.
Lullabies: A Different Mechanism
Lullabies do not primarily work by masking. They work by engaging the baby's auditory and emotional systems in ways that signal "this is a moment of safety and rest." A 2003 study by Shenfield, Trehub, and Nakata found that infant-directed singing reduced infant cortisol over a sustained period, with stronger effects than recorded music. A 2012 study by Trehub and colleagues found that infants showed prolonged calm engagement during live lullabies — markedly more than during speech.
This is why lullabies are often most effective at sleep onset, during the bedtime routine, and during fussy spells where you want to actively shift the baby's state — and why ambient white or pink noise is often more effective for staying asleep through environmental disturbance.
Practically:
- Lullabies during the wind-down routine. Singing or playing the same lullabies as part of bath, dressing for bed, and the final cuddle creates a state cue. After two to three weeks, starting the lullabies begins to shift the baby toward drowsy.
- Lullabies at sleep onset. Many parents transition into the cot with the lullabies still playing. This works fine, with two cautions: keep the volume below 50 dB at the baby's head, and consider whether you want the music to continue all night (most experts recommend it does not, because waking in silence after sleeping in music can briefly disorient a baby).
- Live singing matters when you can manage it. Recorded lullabies are a reasonable substitute, especially when the parent is exhausted or out of the room, but the calming response to live infant-directed singing is consistently stronger across the research. A parent humming along with a recorded track is closer to the live response than the recording alone.
Practical Comparison
| Feature | White noise | Pink noise | Lullabies |
|—|—|—|—|
| Primary mechanism | Masks sudden environmental sound | Masks sound, gentler spectrum | Engages emotional/auditory systems; signals rest |
| Best use | Continuous, low-volume background through naps and night | Same as white noise but better tolerated | Wind-down routine; sleep onset; active soothing |
| Volume target | ≤50 dBA at baby's head | ≤50 dBA at baby's head | ≤50 dBA at baby's head |
| Distance from cot | ≥2 metres | ≥2 metres | ≥2 metres if speaker; closer fine if parent singing live |
| Best paired with | Quiet routine; not as primary settling tool | Quiet routine; not as primary settling tool | Bedtime ritual, parent voice, calming visuals |
| Wean by | ~12 months | ~12 months | Lullabies can continue indefinitely; they are part of bonding, not a sleep crutch |
A Note on Ocean Sounds, Heartbeats, and Womb Sounds
Some sound machines play recorded heartbeat or womb-sound tracks, sometimes pitched as imitating the in-utero environment. The original Heartbeat Bear and similar products have a small evidence base from older studies (Salk 1962, et al.) suggesting reduced crying with heart-rate-tempo audio in the immediate newborn period. The effect tends to be most useful in the first 6–8 weeks and to fade after that, as the baby's auditory environment shifts away from the in-utero baseline.
Ocean-sound and rain-sound tracks are essentially pink-noise-shaped audio with a gentler perceived character. They behave like pink noise for purposes of masking and volume guidance.
What to Use, in One Paragraph
For a baby who wakes at small household sounds: pink noise, ≤50 dB at the cot, 2 metres away, used through naps and nighttime in the first year, weaned around 12 months. For a baby who is fussy at sleep onset or has trouble settling: lullabies during a consistent wind-down routine, with live singing where possible, then either continuing the lullabies or transitioning to silence (or low pink noise) once the baby is in the cot. For a baby who needs both: lullabies for the routine, ambient pink noise for staying asleep — they are not in competition. The volume rule applies to all of it, every time.
Key Takeaways
White noise, pink noise, and lullabies do different jobs and should be chosen accordingly. White noise masks environmental sound but can sound harsh; pink noise is the same masking effect with a softer, more naturally calming spectrum. Lullabies do not primarily mask sound — they engage the baby's emotional and bonding systems and signal sleep. Volume matters more than type: keep any continuous sleep sound at or below 50 dB measured at the baby's head, with the source at least 2 metres from the cot. Lullabies are best at sleep onset and during the bedtime routine; ambient noise is best for staying asleep through household sound.
