More discussion on the Red Hot Chili Peppers iTunes-specific master.
The claim, here:
Apple’s 256 kbps AAC files are supposed to sound pretty close to CD-quality and they routinely fool listeners in double-blind listening tests. But when record-producer/living-legend Rick Rubin heard the iTunes version of his new Red Hot Chilli Pepper production I’m With You, he was reportedly appalled by how its sound changed during the conversion process.
But then here:
The two had to run the masters through a specialized replica of the iTunes Store proprietary AAC encoder using command-line code, because the store’s codec is different than the consumer-grade iTunes converter.
This is the first I’ve ever heard that the iTunes Store AAC encoder is different, and higher quality, than what every iTunes software user already gets.
The article also contests Ian Shepard’s null test.
All of this goes without even mentioning that null tests are only useful in establishing whether or not any difference exists between two files. Null tests however, have not been established as a reliable measurement of how audible those differences are. A blind ABX test would be necessary to give some indication as to which file real-world listeners think is closer to the original.
Also check out Bob Ludwig’s thoughts on Mastering for iTunes (they’re favorable and he explains why).