Finally some explanation direct from the source:
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.
Now this is a little different that just boosting EQs for white earbuds. They are starting with the high resolution audio and encoding that down, rather than going through all that for a CD and then encoding the CD and sending that to Apple. The iTunes Producer software sends your music to Apple to sell in iTunes used to just encode your CD as Apple Lossless and upload it to Apple. Looks like this is changing.
I still get wary when an audio engineer says they’d still pick the CD as the highest quality commercial release. And how, if iTunes is still publishing these songs as 44/16 AAC files, is this different than doing this same downsample and dithering process for a 44/16 CD?1
This bit is interesting. Apple is trying to serve as the archive of nearly all digital masters.
…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.
- Mastered for iTunes
Mastering for iTunes suggests using 24bit/96k source material. Download the free tools including droplet. http://t.co/AzgrClnU— stretta (@stretta) February 24, 2012
Looks like there may be at least a couple of reasons, like built-in soundcheck profiles and 32-bit floating-point files used during sample rate conversion. ↩