Has anyone did a blind test on iTunes AAC vs CD/Lo

Hmm, did not know the iTunes music gets compressed on download, that's interesting. I still think a 256 AAC purchased from iTunes sounds better than one I create myself, there's some tech there that I don't have access to. Of course I haven't tested this with the same track, its just a general statement right now, my impression. I might test this in the future, but for now, I prefer to buy CDs. I like having the media, and I have shelving to fill!

I'm the same way. I prefer physical media. I have pretty sensitive ears and can spot major compression artifacts quickly. But, i'm at a loss with an iTunes downloaded track. At least with the system I have now. I wonder if the above poster actually listened to an ACTUAL iTunes 256 AAC download. If he is hearing artifacts on those files he has some golden ears. I can id pre echo, mild wobbling or distortion with lower resolution tracks as with MP3's at 320. I know the artifacts exist on the AAC's, I just do not have the ability to hear them (yet).

Great topic!
I have been burning at AAC 256, 320, and lossless. I have Martin Logans which are pretty revealing. In blind testing I can hear no differences between CD and lossless, possibly minute differences between CD and 320 AAC but it is extremely close. Slight changes start to appear at 256 and below in terms of high end and low end rolloff, loss of room size, and lack of air. I have settled on AAC 320 for my ipod and using the Pure i-20 dock, have replaced my CD player as my source.

The guys over at hydrogenaudio strongly disagree with this and state that in double blind testing with the latest encoders, AAC 128 and higher is 100% transparent.

I've only heard a 128 Mp3 and there is a big difference over CD. I've never tried a 128 AAC

AAC 128 vs. Redbook on my system... Its not even close. Redbook wins by a long shot. I'll pick the 128kbps rip every time in every blind test, I'll bet. I don't see how anyone can say 128kbps is 100% transparent. But like Shadorne says, you have to know what to listen for. I guess not everyone can (or wants to) tune into those lost details at the low and high end, that is where I hear it. I also hear it during lapses in the music where the song is reduced to a single instrument, like a guitar riff or a bass drop, or a sound effect. Low bit-rate rips kill detail in those passages.
Consider that the bit rate of a lossless AIFF runs at 1411kbps, this is 11 times the bit rate of a 128 AAC. Just like in video compression, quality is all about the bit rate. How much data can the codec push. I rip apple lossless.