I did a blind test with a friend once, 192/320/lossless, and we both could definitely hear which file was 192 - but not which was 320/lossless.
Most of the compression in 320 mp3s is also in areas humans can't hear. I once created a 320 mp3 with a 16kHz cutoff instead of the 20kHz lame uses by default, and to me there was no audible difference - even inverting one and listening to the difference didn't produce anything audible (to me).
Of course nobody uses mp3 anymore, not even iTunes, they encode as 256 aac, which is a far superior codec and near lossless. I doubt anybody can hear the difference between the lossless file and the iTunes file.
Most of the compression in 320 mp3s is also in areas humans can't hear. I once created a 320 mp3 with a 16kHz cutoff instead of the 20kHz lame uses by default, and to me there was no audible difference - even inverting one and listening to the difference didn't produce anything audible (to me).
Of course nobody uses mp3 anymore, not even iTunes, they encode as 256 aac, which is a far superior codec and near lossless. I doubt anybody can hear the difference between the lossless file and the iTunes file.