Usually it's double blinded ABX testing: A computer program gives you: Encoding A, encoding B, unknown encoding A or B. You have to choose if X is A, or X is B.
One of the encodings will be "uncompressed" when testing if the format in question is perceptually lossless.
Repeat that a couple hundred times with many different listeners using standardized samples and programs (doom9, an audiophile forum, does such runs every now and then), and you get a rather good idea on what's going on.
As for the 192kbps: It also depends on the algorithms used. bladeenc or 8Hz-mp3 back then created 320kbps files where you can easily hear the difference. Current lame builds at 192kbps? not so much.
One of the encodings will be "uncompressed" when testing if the format in question is perceptually lossless.
Repeat that a couple hundred times with many different listeners using standardized samples and programs (doom9, an audiophile forum, does such runs every now and then), and you get a rather good idea on what's going on.
As for the 192kbps: It also depends on the algorithms used. bladeenc or 8Hz-mp3 back then created 320kbps files where you can easily hear the difference. Current lame builds at 192kbps? not so much.