Background noise for falling asleep.

Why it works

Background noise for sleep has one job, which is to be unremarkable for a long time. A fan is the classic choice because it is low, steady and domestic. This one is built from filtered noise and two faint motor tones while it plays, so it never loops and has no adverts, having no video to put them in.

A background needs a foreground. With nothing in front of it, your own thoughts step forward, and they are seldom restful at this hour. If you would like to choose the foreground, there is a slow story on the second fader. It is content to be half heard.

What you are hearing

• Warm fan hum. Brown noise low-passed at 240 Hz for the moving air, with two faint tones at 60 and 120 Hz underneath for the motor.
• The voice. The first four minutes of Aristotle, the Greatest Philosopher, a Lullable story, in a synthesised voice. It only plays if you bring it in.
• The ending. The preview lasts four minutes. Its last ten seconds are a straight fade to silence, so it never stops abruptly.

For a real recording that runs forty minutes, the Lullable iPhone app has rain, waves, a campfire and plain noise, with no voice and no music.