Soft white noise, with no loop to find.

Why it works

White noise has equal energy at every frequency, which is why it masks nearly anything and why it can feel like a lot. This version removes the sharpest part, above 4,000 Hz, and is generated fresh while it plays. A recorded loop of it has a seam. A stream of random numbers does not.

The seam matters more than it should. A mind that is awake at night is very good at patterns, and a three-minute loop is a pattern. Even without one, pure noise is a thin diet. Try it with a story underneath your attention, told slowly, and see which you are still listening to at the end.

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.