Brown noise for sleep, with no loop in it.

Why it works

Brown noise is white noise with the top taken off. Its energy falls by six decibels for every octave you climb, which leaves a low, even wash, closer to a distant waterfall than to radio static. This one is computed sample by sample while it plays. Nothing is recorded, so nothing comes round again.

It covers a room well. What it cannot do is give a mind anything to hold, and a mind with nothing to hold tends to supply its own material. Slide the voice in and you will hear the difference: a slow, true story, its ending given away at the start, resting on the same sound.

What you are hearing

• Brown noise. White noise run through a leaky integrator, so its energy falls six decibels per octave, then low-passed at 400 Hz. A low, even wash.
• 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.