Sleep sounds
A mix built for the room to be quieter than the sound rather than louder than it, and a sleep timer that fades out gradually — because a sound that stops abruptly is itself the kind of change that wakes people.
Masking is about change, not about silence
The useful mental model is this: sleep is disturbed far more reliably by a change in sound level than by a constant level. A refrigerator that has hummed all night does not wake anybody; the moment it stops, people stir. A steady background sound works by shrinking every change relative to what is already there — the car door at 3 a.m. is the same 50 dB event, but against a floor of 35 dB it is a much smaller step than against a floor of 20.
That reasoning also tells you when it will not help. In an already quiet bedroom there is nothing much to mask, and you are adding sound to a silent room. Plenty of people sleep worse that way, and this is the most common reason a sound machine disappoints: it was solving a problem that was not there.
It also tells you how loud to set it, which is the question people get most wrong. The sound only has to be a little above the disturbances you want covered. Loud enough to notice is loud enough to be a disturbance itself, and much louder than that is a hearing exposure question rather than a sleep question.
Why the timer fades instead of stopping
A timer that cuts the sound dead recreates the exact event it was there to prevent. Falling asleep takes most people fifteen to twenty-five minutes, and the transition into deeper sleep is not instantaneous — a hard stop at the forty-minute mark lands in the middle of it. So the last tenth of every session here is a fade, capped at two minutes and never shorter than ten seconds, following a raised-cosine curve that eases at both ends rather than ramping linearly into silence.
The same curve is used when starting, which is the safety half of the same idea. Press play and the master gain rises from silence over about two seconds. Combined with a master volume that starts at 20 per cent, that is what stops the site delivering a sudden full-level noise into headphones somebody left turned all the way up — a real risk with any audio tool, and one that no wording anywhere on the page would mitigate.
If you want sound for the whole night, leave the timer off and it runs until you close the tab. Browsers may suspend audio in a background tab on some phones; keeping the tab in the foreground with the screen off is the reliable arrangement, and a device plugged in, since generating audio continuously does use the processor.
What each timer setting actually schedules
The last tenth of every session is a fade rather than a cut, capped at two minutes. These numbers come from the scheduler itself, so the table and the behaviour cannot disagree.
| Timer | Full level for | Then fades over |
|---|---|---|
| 15 min | 14 min | 90 sec |
| 30 min | 28 min | 120 sec |
| 45 min | 43 min | 120 sec |
| 60 min | 58 min | 120 sec |
| 90 min | 88 min | 120 sec |
| 120 min | 118 min | 120 sec |
The fade follows a raised-cosine curve that eases at both ends and finishes at exact silence, so nothing stops with a click.
Common questions
How long should the sleep timer be?
Thirty to forty-five minutes suits most people, which covers falling asleep with some margin. If you tend to wake in the small hours, running it all night is a reasonable alternative — set the timer to off.
Which sound is best for sleeping?
There is no general answer, but the reliable starting point is rain with a little brown noise underneath, which is the preset on this page. Try each of the others for a couple of minutes before deciding.
Will it keep playing if my screen turns off?
Usually yes on a desktop, and it depends on the phone. Some mobile browsers suspend audio when the tab loses focus. Keeping this tab in the foreground with the screen locked works on most devices.