Oh dear. We won't name names, but of the seven people tested, including five members of the TrustedReviews team, only one person could accurately pinpoint which tracks were MP3 and which tracks were FLACs in every case. Of the rest, three of our subjects managed to pick the lossless track on two occasions, while the other three only managed a single correct choice.
Interestingly, the results didn't come out as we anticipated. We knew that discerning 320kbps MP3 files from lossless FLAC files was going to be hard, but we expected that, with decent listening equipment and a couple of hearings, most of the test subjects would be able to tell a 192kbps MP3 from the FLAC original. Shockingly, this wasn't so. In the tests where we played 320kbps files against FLACs the number of people who chose correctly and incorrectly were equal. In the tests where we played 192kbps files against FLACs, more of our subjects actually went for the lower-quality file.
Does the style of music make any difference? Certainly Massive Attack's dark, heavily layered sound seemed to wrong foot our panel more than the R&B, rock and classical tracks used. One subject even noted that the 192kbps version sounded clearer, but also flatter, as if the sacrifice of some background tone made what remained seem that little bit more defined. With certain styles, it's also easier to hear certain cues that tell you that the file has been compressed. With Radiohead, for example, those who got it right noted that the percussion - specifically - the cymbals, sounded smeared and less well defined in the 192kbps track as opposed to the FLAC version. This difference isn't so pronounced when you go up to 320Kbps.