Green noise vs brown noise, in one player.

Why it works

Green noise sits in the middle frequencies, around 500 Hz, and tends to sound like water or foliage. Brown noise sits lower and sounds like distance: surf from a mile inland. Green survives a phone speaker. Brown mostly does not, so if you are listening without headphones, that may decide it for you.

They do the same job in different registers, and the job is covering sound. If what is keeping you up is the room, pick the one you like. If it is the day you just had, a colour will not reach it. A story sometimes will.

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.
• 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.