Green noise for a busy mind.

Why it works

Green noise lives in the middle of the spectrum, where rivers and trees put most of their sound, and it comes through small speakers better than the deeper colours. This one is filtered pink noise, made as it plays. It is as close as arithmetic gets to an open window on a mild night.

A busy mind at an open window is still busy. The sound gives it a pleasant place to be busy in. If you would like it to slow down as well, give it one thing to follow at walking pace. The story on the second fader moves at about that speed and gets quieter as it goes.

What you are hearing

• Green noise. Pink noise passed through a wide band centred on 500 Hz. The lows and the hiss are both turned down, leaving the middle, where most outdoor sound lives.
• 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.