PBS produced this interesting video about digital v. analog sound and recording. Glean what you want from this video, but listening tests in my mind are worthless. For example, when I first got my an iPod I ripped music to it at 320 kbps in AAC format and I thought it was equal to my CDs. After listening to the songs for a while I got fatigued and the quality inferiority became more evident the more I listened. So, I tried uncompressed AIFF files and never looked back. I guess what I am saying is ABX testing has severe limits when it comes to audio.