Brown noise
Deep, soft rumble like distant surf. The most popular noise for sleep right now because it masks sound without the hiss.
Brown noise has most of its energy in the low frequencies, so it sounds deep and rounded rather than hissy. Many people find it the easiest noise to fall asleep to, and it's popular for focus too.
Tip: keep the volume low, around the level of a quiet conversation, and set the timer so it fades out after you're asleep. On a phone, keep the screen on or the browser may pause the sound.
10-hour versions that fade to a dark screen are coming to our YouTube channel.
Other free sleep sounds
White noiseBright, even hiss that's best at covering voices, traffic and sudden soundsPink noiseSoft and balanced, like steady rainRain soundsSteady rain on the roof, generated live so it never repeatsOcean wavesSlow waves rolling in, the way Bondi sounds at nightFan soundsThe familiar bedroom fan hum, without the cold air in winter
Want to mix several sounds at once? Try the full sound mixer.
Still can't sleep?
Have a look at the Sleep Kit, sorted by what's keeping you up.