What the new review found
The 2026 review by Henriques and colleagues included 15 studies involving 2,024 hospitalized adults. Ten were randomized controlled trials and five used quasi-experimental designs. Most took place in intensive-care settings. The interventions varied widely: some used calming music, some used nature sounds, and others used white noise. Listening periods ranged from a few minutes to the whole night.
Across the studies, sound-based interventions were associated with better reported sleep quality. That is promising, especially because poor sleep is common in hospitals and non-drug options are valuable.
However, the studies were highly inconsistent. The pooled result had very high statistical heterogeneity, meaning the size of the apparent benefit differed greatly from one study to another. There was also no clear agreement on the best sound, volume, timing or duration.
Reported sleep is not the same as measured sleep
Most studies in the review relied on questionnaires: patients were asked how well they thought they had slept. That matters. Feeling less disturbed, more comfortable or calmer can be a worthwhile outcome in itself.
But a questionnaire cannot show exactly how much time someone spent in light, deep or REM sleep. Those questions require sleep-stage assessment such as polysomnography; ordinary consumer tracker estimates are not equivalent. A relaxing response also does not prove that a sound changes brain waves in a predictable way.
This distinction is particularly important for claims about delta waves. Delta activity is associated with deep non-REM sleep, but playing a low-frequency tone or labeling music “delta” does not establish that it will create deep sleep. That would need direct physiological evidence from well-controlled studies.
Why a sound may help in a noisy environment
One plausible explanation is masking. A steady background sound can reduce the contrast between a quiet room and sudden noises such as a door closing or a passing vehicle. The interruption is still present, but it may stand out less.
Masking is a practical acoustic idea, not proof that the added sound improves sleep biology. A 2021 systematic review of continuous noise as a sleep aid found that the overall evidence was very uncertain. Some studies suggested benefit, while others found no effect or possible disruption. The reviewers concluded that the evidence was too weak to recommend continuous noise confidently as a general sleep treatment.
Hospital findings also may not transfer neatly to a home bedroom. Hospital patients may be dealing with pain, medication, anxiety, alarms and clinical care. In a quiet bedroom, adding sound could be unnecessary—or distracting—for some listeners.
A more useful question: what are you trying to soften?
Instead of asking which colour of noise is “best,” start with the sound problem in the room.
- For irregular traffic, voices or doors, a low, steady background layer may make sudden changes less noticeable.
- For an already quiet room, gentle nature ambience or music may be more useful as part of a wind-down routine than as all-night masking.
- If a sound keeps drawing your attention, lower it, simplify the mix or turn it off. More sound is not automatically better.
Keep the level comfortable and well below anything that feels forceful. Avoid raising the volume simply to overpower every external noise. If you only need audio while settling down, a timer or gradual fade may be preferable to continuous playback.
Building a simple bedtime mix
Begin with one stable layer rather than several competing textures. You might choose soft rain, ocean ambience or a noise colour, then add a quieter musical element only if it makes the atmosphere feel more comfortable.
In MindTuned Sleep Studio, you can adjust layers independently, save a preferred mix and use the sleep timer with a gradual fade. Treat the controls as a way to find a personal, comfortable balance—not as a prescription or a guaranteed route to sleep.
The takeaway
The newest hospital evidence suggests that sound can improve perceived sleep for some people in noisy clinical environments. The result is useful, but not definitive: the studies used different sounds and methods, mostly measured self-reported sleep, and produced widely varying results.
For home listening, the most responsible approach is modest and personal. Use sound to soften a specific disturbance or support a familiar bedtime routine. Keep it quiet, notice whether it genuinely helps, and do not assume that a frequency label tells you what is happening inside the sleeping brain.
Research cited
This article is for general education and is not medical advice.