Apple has officially launched iTunes Plus, its online source for DRM-free music tracks encoded in high quality 256kbps AAC.

iTunes Plus currently offers EMI’s entire digital catalogue, including singles and albums from Coldplay, The Good, The Bad and The Queen, The Rolling Stones, Norah Jones, Frank Sinatra, Joss Stone, Pink Floyd, John Coltrane and more than a dozen of Paul McCartney’s classic albums available on iTunes for the first time.

As previously reported, songs cost just 99 pence each. Along with the new service, iTunes will continue to offer its entire catalogue, currently over five million songs, in the same versions as today - 128 kbps AAC encoding with DRM - at 79 pence per song.

iTunes customers can also upgrade their library of previously purchased EMI content to iTunes Plus tracks for just 20 pence a song, or £2.00 for most albums. However, this feature doesn't appear enabled at time of writing.

“Our customers are very excited about the freedom and amazing sound quality of iTunes Plus,” said Steve Jobs, Apple’s CEO. “We expect more than half of the songs on iTunes will be offered in iTunes Plus versions by the end of this year.”

“This is a tremendous milestone for digital music,” said Eric Nicoli, CEO of EMI Group. “Consumers are going to love listening to higher quality iTunes Plus tracks from their favourite EMI artists with no usage restrictions.”

iTunes is also offering customers a simple, one-click option to easily upgrade their library of previously purchased EMI content to the iTunes Plus versions. EMI music videos are now also available in iTunes Plus versions with no change in price.