Why a white noise loop can keep you awake.

Why it works

White noise is meant to be patternless. A recording of white noise is a few minutes of patternlessness played again and again, and the join is a pattern: a faint click, a shift in tone, a texture you have met before. A brain awake at night is a pattern detector with nothing else on, and it will find the join.

The noise on this page is generated while it plays, so there is no join. That solves the loop. It does not solve the rest, which is that a mind left alone with a featureless sound still goes looking for work. For that, try the second button, and give it some.

What you are hearing

• Soft white noise. True white noise, equal energy at every frequency, with the sharpest part above 4,000 Hz taken off so it is easier to live with.
• 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.