Yes, looking for artifacts is one way, but if the MP3 encoding was done at a high enough quality it's nearly indistinguishable from the original. Same with JPG images at 100% quality. Do you want me to show you ugly degradation visible to the naked eye in 100% jpgs ? Here is one. It's some artwork I am doing. It's in true color png (lossless). Convert it to 100% jpg and see what I mean. Huge loss of quality. http://stashbox.org/uploads/1150207339/Master%20001s.png As for audio it is the same I believe as lossy is not lossless, but without an original to do an ABX test with, it may be hard to say. So the above artifact identifier is probably the best method without originals. Hydrogen Audio is the best place for that type of question anyway. http://www.hydrogenaudio.org/forums/index.php Perhaps your JPG encoder's "100%" isn't the same as mine... and your test sample looks like it was designed to test the limits of the encoder (nice art btw). Here, for your enjoyment, is a JPG created from your above sample at 100% quality level: http://img107.imageshack.us/img107/6702/master001s2pl.jpg@Elektrik: I definitely see a difference, but all MP3 encoders are not created equal, just as JPG encoders I demonstrated above.