Brown noise, pink noise or binaural beats: which sound does what

Apple Music now layers frequencies under pop songs and calls it sound therapy. The vocabulary has gone mainstream faster than the evidence. Here is what each sound is for.

Sophie Kazandjian
May 2026 · 7 min read

Part of: The Science →

In May 2025 Apple and Universal launched a collection called Sound Therapy: hits by Katy Perry and Imagine Dragons with sound layered underneath, sorted into Focus, Relax and Sleep. The labels on the tin were gamma, theta and delta, plus white and pink noise. I have spent a lot of time explaining those words to people who bought the app, and I have mixed feelings about the world's biggest music company doing it for me. The vocabulary is now everywhere, which helps. The labels, though, sound like they describe brainwaves, when what they describe is how the audio is modulated, and the evidence behind each is very uneven.

The colours first, because they are the simplest. White noise has equal energy at every frequency and sounds like a detuned radio. Pink noise tips the balance toward the low end, so it sounds like steady rain or a waterfall. Brown noise tips further still and sounds like a distant river or a plane cabin, deep and soft. None of these are frequencies in the sense a solfeggio tone is; they are textures, and the ear treats them as a blanket that covers other sounds.

Pink and brown noise for falling asleep

The masking effect is the one with the most support, and it is modest. A 2021 systematic review found 38 studies of continuous noise as a sleep aid and rated the evidence as very low quality: small samples, mostly self-report, some showing faster sleep onset, others no effect, a few suggesting the noise itself fragmented sleep. The clearest positive trial put eighteen healthy adults to bed ninety minutes earlier than usual, a model of the night before an early flight, and filled the room with a soft broadband sound at 46 decibels; they fell asleep 38 per cent faster than in silence. The sound was a pink-noise-like masking spectrum, the study was one night long, and a sound-masking company paid for it.

So if the problem is getting off to sleep in a noisy flat or with a partner who snores, pink or brown noise at a low level works well, and the choice between them is taste. Brown is the one people describe as calming, and it has almost no research of its own: the only study I found that named it measured pupil responses to ten-second bursts and found no difference from white or pink. The ADHD community adopted brown noise for focus with real enthusiasm, and the 2024 meta-analysis of noise and attention in young people found a small benefit from white noise in those with attention difficulties and a small cost in those without, with no eligible study of brown at all.

Pink noise and deep sleep

Pink noise has a second, more interesting use, and it is the one Apple's "delta plus pink noise" label is gesturing at. The slow waves of deep sleep, the ones the delta sleep article ties to collagen, run at under one cycle a second, and in 2013 a German team played eleven young adults short bursts of pink noise timed to land on the rising phase of each slow wave. The waves grew, the sleep spindles that ride on them increased, and the participants remembered more word pairs the next morning. A Chicago group repeated the design in 2017 in thirteen older adults and found slow-wave activity up and overnight recall improved by a quarter. This is the origin of every "deep sleep" sound claim you will see.

The catch is the word timed. Those bursts were triggered by an EEG reading each person's brain in real time. A pink noise track playing continuously through the night is not doing that; it is masking, which is fine, and it is not enhancing slow waves, which is what the studies showed. A 2021 meta-analysis of the timed approach found the memory benefit shrank to a trend across ten studies and concluded the evidence did not yet support the consumer headbands being sold on it.

Binaural beats before sleep

Binaural beats are a different mechanism altogether. Play 108 Hz in the left ear and 115.83 Hz in the right, through headphones, and the brain hears a pulse at the 7.83 Hz difference, the Schumann frequency the app uses in its second step. The beat is created inside the head, which is why the effect needs headphones and vanishes through a speaker. The evidence is reviewed in the sound healing article: a 2019 meta-analysis found a medium effect across anxiety, attention and pain, theta-range beats were the ones most associated with lower anxiety, and whether the brain's own rhythms follow the beat is still contested. One small three-night study in Thailand played a 3 Hz beat from the moment participants entered light sleep and found their deep sleep rose from 91 to 126 minutes; that was fifteen people in one lab, and it has not been repeated.

The app uses beats in its deeper stages because the evidence, though small, points the right way: theta and delta beats have the best record for the drowsy state you want before sleep, and pink or brown noise is the texture that makes them comfortable to lie under. The two do different jobs, so they can be combined.

Which sound to use, and when

To fall asleep against noise, pink or brown, low, from a speaker or headphones, and stop worrying about which colour; the sleep article covers the rest of the bedroom. For work with a busy mind, white or brown, and notice after a week whether it is helping or just present. Before bed, a theta-range binaural beat over a soft noise bed, through headphones, lying down, for a fixed twenty minutes. As for the deep-sleep enhancement, nothing you can buy yet does what the timed studies did, so treat the deep-sleep labels as a promise rather than a result.

The routines in the app were built as that third case, with the noise bed under the beat, and the free taster runs the sequence in ten minutes if you want to hear what the words mean. Whatever Apple does to Katy Perry, the question underneath is the one the studies keep asking, whether a body lying still under steady sound settles faster than one lying in silence. On that, at least, the answer has been yes for as long as anyone has measured it.

Try it free →

To hear the third case in practice, a theta-to-delta beat over a brown-noise bed with the app’s rain soundscape underneath, this is an hour of it.

ON YOUTUBE · 1 HOUR

7.83 Hz sleep track: Schumann, then theta, then delta

An hour for bedtime. Fifteen minutes at 7.83 Hz, twenty at 4 Hz theta, twenty-five at 2 Hz delta, over a quiet bed of brown noise, the app's own sound engine. The screen dims after five minutes.

Watch on YouTube →