Apple is developing an automatic volume control device for iPods amid growing fears that its users are at risk of hearing damage from listening to loud music.

The next iPods and iPhones could automatically calculate how long a person has been listening and at what volume, before gradually reducing the sound level.

The device will also calculate the amount of “quiet time” between when the iPod is turned off and when it is restarted, allowing the volume to be increased again to a safe level.