Apple made a maximum volume setting available in its iPod software update released on Wednesday following complaints and a lawsuit saying the popular player can cause hearing loss. The free download applies to the iPod Nano and the iPod models with video-playback capabilities. Parents will also be able to set a locked limit on their child's players with a code.

Greg Joswiak, Apple's iPod Marketing Vice President, said it was responding to "increased attention in this area. We want to offer customers an easy to use option to set their own personal volume limit," he said.

The company has posted online a brief analysis about sound, advising users of iPods, computers and other devices to adopt common sense and "listen responsibly" when using headphones or earbuds.

Earlier this month, the U.S.National Institutes of Health said new studies were needed into the effects of in-ear headphones.

It was responding to calls by U.S. congressman Edward Markey for research into the possible long-term effects of loud music on hearing. Health experts in general want more studies into the effect of earphones.

Apple is furthermore facing a U.S.legal action claiming its iPod can damage hearing. John Kiel Patterson, of Louisiana, is suing Apple in the U.S. District Court in San Jose, California.

He says his iPod is capable of generating more than 115 decibels, a dangerous noise level if a person is exposed to the sound for more than 28 seconds a day.

Although the iPod is more popular than other types of portable music players, its ability to cause hearing loss isn't any higher, experts said.