Audio Format Listening Tests Concluded
Pointing to the conclusions of this listening study, nullity writes: "The results are interesting, and show a high variation in the performance of the various codecs on different musical styles. Ogg seems to work well on dance music, WMA8 on chamber music, etc."
These tests are all at 64 kbps and most people use much higher bitrates for real music. I'd like to see comparisons at 128k bits minimum, and preferably 160k or 192k, which is what most quality mp3's are at, for direct comparison.
This is an interesting and relatively well done test (although it appears that the listeners knew which format they were listening to, so it wasn't truly double-blind, and a anti-MS and pro-Ogg bias can't be ruled out).
However, some discussions seem to be focusing on this saying AAC is bad or WMA is bad, when really it refers to the particular implementations in codecs of those formats.
For example, the Apple MPEG-4 AAC-LC encoder was used for AAC. This is a Low Complexity version of the format. Also, the Apple encoder has a strange limitation where it automatically converts 44.1 stereo to 32 stereo at that data rate. This isn't required by the AAC format. Other AAC encoders yield MUCH better results, and beat MP3 Pro in double-blind testing. I haven't seen any double-blind comparisons between AAC and Ogg.
Also, the WMA8 encoder is due to be replaced by the backwards-compatible WMA9 in early September. Of course, there may well be improved versions of the other encoders by then as well.
My video compression blog