The 'Mastered For iTunes' Deception
People speak of not noticing the difference in audio between music downloads and physical copies, whereas chances are they have. In a crystallising moment, there will always be that tiny split-second noise of digitisation, or the compromised sound-levellings of an alternate bit rate, courtesy of an encoder. It's that unavoidable glitch in the song that you can't un-hear when it is heard, and builds a somewhat undefinable character around the song.