Mastered For iTunes
We’re committed to delivering music exactly as the artists and sound engineers intend it to be heard. Housed here are the information and tools necessary to create the highest-quality masters for iTunes. Learn more by reading the Mastered for iTunes technology brief.This is certainly worth a read and not nearly as evil as one might have thought. You can go to the Apple webpage or download the "Mastered for iTunes" PDF.
Here's my favorite part (with emphasis added):
To take best advantage of our latest encoders send us the highest resolution master file possible, appropriate to the medium and the project.Some day (maybe soon?) Apple Inc. will flip that big 24/96 switch and let the HD love flow.
An ideal master will have 24-bit 96kHz resolution. These files contain more detail from which our encoders can create more accurate encodes. However, any resolution above 16-bit 44.1kHz, including sample rates of 48kHz, 88.2kHz, 96kHz, and 192kHz, will benefit from our encoding process.
Don’t upsample files to a higher resolution than their original format. Upsampling won’t recover or add information to an audio file. Don’t provide files that have been downsampled and dithered for a CD. This degrades the file’s audio quality.
As technology advances and bandwidth, storage, battery life, and processor power increase, keeping the highest quality masters available in our systems allows for full advantage of future improvements to your music. Also, though it may not be apparent because there may not always be a physical, tangible master created in LP or CD format, the iTunes catalog forms an important part of the world’s historical and cultural record. These masters matter—especially given the move into the cloud on post-PC devices.