If you fire up iTunes on your iPhone, iPad or computer, you’ll see that there is a brand new section inside the store called “Mastered for iTunes”. This way Apple tries to deliver best possible audio quality encoded files for all those details inside the tunes.
Audio files are delivered in iTunes Plus format which has a variable bit rate of 256 kbps for the AAC file format (compared to 128 kbps AAC files available in the early days). Publishers will be able to submit better quality recordings and the end user, regardless if we talk about your average listener or an audiophile, will benefit from enhanced quality music files which sound the way the artists intended them to. If you’re interested in technicalities, check out the white paper at the source link below.