* The article covers digital audio from its very foundations, which is unnecessary. Just put a link to Wikipedia.
* The citation format is weird. Instead of using inline hyperlinks, you have to look up references at the end.
* The test only covers MP3. This is 2014... and we know MP3 has a low-pass filter.
* The methodology doesn't mention converting from MP3 back to a lossless format for the ABX test, and it doesn't mention measuring MP3 encoder gain. ABX tests can be colored when people recognize differences between lossy and lossless playback that have nothing to do with the encoding itself: if lossless playback uses less IO and more CPU, then you might hear less clicking from your disk drive and your computer's CPU fan might spin faster. Most ABX tests convert both files back to WAV before testing.
* The spectrum of the residual is not very interesting, because the human ear is not sensitive to phase (or far less sensitive to phase than amplitude). It would be more interesting to compute the differences in the spectrums.
If you want a more sound and thorough analysis of audio compression, try the Hydrogen Audio tests:
http://wiki.hydrogenaud.io/index.php?title=Hydrogenaudio_Lis...
Quick summary: At reasonable bit rates, many encoders are sonically transparent. At lower bit rates (64/96 kbit/s), Opus is the most transparent, and Apple's encoder is in second place.