This is a fairly good look at the AAC encoding guidelines set forth by Apple.
The quote below discusses the subjective and empirical results of the process. It seems to have an affect for at least some material. The "mastered for iTunes" waveform was closer to the original CD waveform than the ripped AAC file.
I'm not an iTunes user and own no AAC encoded songs, but I have subjected myself some testing against MP3 and found that 128k CBR is generally good enough for me. 256k is inaudible in all but the most killer of samples. It's my understanding that AAC is considerably better than MP3 and killer samples are more difficult to come by. If the mastering techniques outlined above continue to evolve and improve, the loss from 256k AAC should be inaudible to all but the most gifted listeners.
The quote below discusses the subjective and empirical results of the process. It seems to have an affect for at least some material. The "mastered for iTunes" waveform was closer to the original CD waveform than the ripped AAC file.
Quote:
We [compared] the original CD master, the file generated by iTunes from that master, and our own "specially mastered for iTunes" version. Subjectively, our tweaks made the track sound better. Much of the "boxiness" was gone, and the song sounded more "alive."
To make sure we weren't hearing things, though, we repeated Shepard's null test experiment. As with Shepard's test, comparing the CD master to a straight iTunes rip produced quite a bit of warbled noise and static. But the null test done with our own specially mastered version was very nearly silent. A few audible bits of music and vocals remained, but the result was much quieter than the noise we heard in the previous comparison.
To make sure we weren't hearing things, though, we repeated Shepard's null test experiment. As with Shepard's test, comparing the CD master to a straight iTunes rip produced quite a bit of warbled noise and static. But the null test done with our own specially mastered version was very nearly silent. A few audible bits of music and vocals remained, but the result was much quieter than the noise we heard in the previous comparison.
I'm not an iTunes user and own no AAC encoded songs, but I have subjected myself some testing against MP3 and found that 128k CBR is generally good enough for me. 256k is inaudible in all but the most killer of samples. It's my understanding that AAC is considerably better than MP3 and killer samples are more difficult to come by. If the mastering techniques outlined above continue to evolve and improve, the loss from 256k AAC should be inaudible to all but the most gifted listeners.









knowing full well that we are more interested in 24/192. I saw something on this topic. Rush's next release "Clockwork Angels," is behind enhanced for iTunes. Once I saw that it will also be released on HDtracks, at 24/96, I lost all interest in ITunes. Besides the focus on mastering for iTunes appears to enhanced the sound for stuff like computer speakers. Personally I hope to avoid anything mastered for iTunes that has some kind of bass boost, to make computer speakers sound better.
