Audio codec blind test by yourself.

http://soundexpert.org/testing-room

This interesting website provides blind test to compare between lossless wave audio with mp3 or aac encoded one. In the wave file they provide, there are two tracks of exactly same music, but with different encoding. One is the original wave track, but another one is AAC or MP3 encoded track. They won't tell you which one comes first, so that you will guess what is what.

Using the tested statistics gathered from the public including yourself, they show and compare the quality of the encoding codec.

It's fun, and even you can test your hearing and sound equipment!