Apple has confirmed that it is investigating problems in updating some iPods, and that its new lossless audio feature is compatible only with third-generation iPods and iPod minis.

iTunes 4.5 introduced a new feature – the Apple Lossless Encoder – which the company says "lets you enjoy the full quality of uncompressed CD audio at half the size". It's aimed at audiophiles who feel that compressed audio sacrifices quality and loses valuable slices of tone.

The company last night said: "If you update your iPod or iPod mini by running the iPod Updater 2004-04-28, you'll be able to enjoy that quality in your third-generation iPod or iPod mini."

The need for a third-generation iPod was not clarified initially when the feature was announced.

Some iPod-owners installing the software have experienced problems, reports claim. It seems that when they attempt to update their music player the software is unable to detect their music player.

Apple's forum carries several reports from iPod users facing problems. One explains: "Tunes 4.5 won't recognize my original 10GB iPod, I am unable to install the updater. The iPod appears mounted in Finder and the iPod screen shows it is mounted but neither the updater nor iTunes 4.5 recognizes it."

Another says: "It has rendered my 3G 15GB iPod useless – it pops in and out of Folder Exclamation and the Apple Logo and when put in the Dock it puts itself into disk mode, but it will not mount on the desktop. The computer will not even recognize the hard drive. Every time I try to restore the software it locks up my G4 tight as a drum. I've even tried going back to 2.1 or 1.3 with the same results. I'm on hold with support as we speak."

Apple issued a statement saying: "Apple is aware of a few isolated reports and is looking into it. Those who encounter a problem should contact AppleCare."