Jim, it is based upon the kbps.
Think of it as regular tv channels vs HD tv channel. For me, the HD channels have better picture but the sound is much quieter then others. This allows for your receiver to do the work, resulting in better sound.
The best solution for this, would be to convert your own music files. This will allow you to select the appropriate speed.
Edit:
Picked up a 3TB harddrive yesterday. Seeing as my 500gb sata, and 1TB are currently full.
So now I have 4.5tb of space
This post was edited by gazeifiee on Oct 12 2011 11:35am