I've done very careful testing and I've found at 256 and above AAC becomes completely transparent with all music. MP3 LAME is transparent at 320. I set up a test with three different codecs Frauenhofer MP3, LAME MP3 and AAC) and three different bitrates (192, 256 and 320) and gave it out to a lot of people. No one could tell the difference between 320 and lossless. Most couldn't tell 256. Some couldn't even tell 192. If you would like to put your observations to the test, I would be happy to give you a blind test to try and see how you do.