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Stillnight.

About the sounds

What we know, and what we don't

Many people find steady sound comforting, and it can mask sudden noises. The research, though, is limited and mixed. Here is our honest reading of it.

The evidence, plainly

A 2022 systematic review of auditory stimulation and sleep found that studies of continuous noise were generally small and of low quality, and the evidence that it improves sleep was weak [1]. A more recent review reaches similarly cautious conclusions about how certain we can be [2].

No colour of noise has been shown to be best for sleep. Stillnight doesn't claim one is, and the app has not been clinically tested. If sleep problems persist, a clinician is the right person to talk to.

White, pink and brown

The "colours" describe how a sound's energy is spread across low and high frequencies. Preference is personal — try each at a low volume.

  • White

    Equal energy at every frequency. It sounds bright and hissy, like untuned radio static.

  • Pink

    Energy falls as frequency rises, so the highs are softer. Often described as balanced, like steady rain.

  • Brown

    Falls off faster still, leaving mostly low tones — a deep rumble, like distant surf.

How the sounds are made

Nothing is streamed or pre-recorded. When you press play, your browser generates the sound on your device using the Web Audio API.

  • Noise starts as random values. Pink and brown are made by filtering that randomness so the higher frequencies fall away. A 20-second segment is looped with a half-second crossfade so there's no audible seam.
  • Rain is band-filtered noise with a very slow swell and a brighter, sped-up layer for droplet texture.
  • Airflow is low-passed deep noise with a gently moving filter, which gives the soft "whoosh" of a distant fan.
  • A gentle compressor smooths peaks. Baby mode limits in-app output to 30% of normal — but your device's volume still determines how loud it really is.

These are synthesized approximations, not recordings of real rain or fans.

Babies and children

The American Academy of Pediatrics recommends care with noise exposure in young children [3]. A 2014 study of infant sleep machines found some could exceed recommended levels at maximum volume and close range [4]. Keep any device far from the cot, at a low volume, and for a limited time. A phone cannot be reliably calibrated to a safe decibel level by an app.

Sources

  1. [1]Capezuti E, et al. (2022). Systematic review: auditory stimulation and sleep. Journal of Clinical Sleep Medicine. PubMed 34964434 (opens in new tab)
  2. [2]A more recent systematic review of sound and noise interventions for sleep. PMC12202548 (opens in new tab)
  3. [3]American Academy of Pediatrics (2023). Preventing Excessive Noise Exposure in Infants, Children, and Adolescents. Pediatrics 152(5). Clinical report (opens in new tab)
  4. [4]Hugh SC, et al. (2014). Infant sleep machines and hazardous sound pressure levels. Pediatrics 133(4). doi 10.1542/peds.2013-3617 (opens in new tab)

Educational information only — not medical advice.