White noise vs a fan. They are not the same.

Why it works

White noise machines and fans are often spoken of as one thing, and they are close to opposites. White noise is brightest at the top of the spectrum. A fan puts nearly everything at the bottom, with a motor tone beneath. If white noise has always irritated you slightly, a fan may be what you were after.

Either will mask a corridor or a snoring dog. If the thing you need masked is the conversation you keep replaying, masking is the wrong tool, and a gentler conversation is the right one. One that is slow, one-sided and about Aristotle is included.

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.
• Warm fan hum. Brown noise low-passed at 240 Hz for the moving air, with two faint tones at 60 and 120 Hz underneath for the motor.
• 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.