here is a blind audio test to challenge you. i have taken two audio files from Liquid Tension Experiment and made two copies of each. one copy of each was encoded to MP3 format using LAME 3.97b using "-V3 --vbr -new" settings, resulting in average bitrates of 184 kbps for "osmosis" and 169 kbps for "paradigm shift". then i decoded the MP3 files back to WAV format (which introduces no further information loss). i reset the dates and times of all files to be identical, then gave them "a" and "b" names at random. the file sizes are identical as well, so there's no help there.
your task is to listen to each pair of files and tell me which (a or b) is the original WAV and which was encoded to MP3. here are the files: