I've anxiously been testing and reading about the quality, performance and size compromises when switching from MP3 to AAC for encoding CDs. Apple's new iTunes Music Store has set a 128k bit rate standard using AAC. Some reports I've read claim that the music downloaded from the iTunes site seem to have been encoded using a higher quality AAC encoder than the one provided with iTunes 4.0 or QuickTime 6.2. I'm anxious to do some simple testing at this end.
But a great, yet simple and easy to understand review by Gunnar Van Vliet
reveals some interesting notes about the differences between encoders. Especially interesting to me was the fact that Gunnar finds that at higher bit rate the 128, the MP3 actually sounds better than AAC. Yet, at the 128 standard of the iTunes Music Store, the AAC is head and shoulders above MP3.
For me, I've been encoding MP3s at 256 VBR using the iTunes encoder at highest quality. This yields significantly larger file sizes, but at least they're playable on my iPod. Gunnar suggests that the file sizes may be comparable to AIFF (CD-quality) are similar and that anyone encoding at this right may as well simply save at AIFF. But this is a moot point since I don't believe the iPod will play AIFF files.
I'd be interested in hearing any readers' experience with the AAC, MP3 and other encoders and would like to post a follow up review here sometime later in May. Reply on the comments section at the bottom of this post or to my email here.