You probably saw it. It's called "Mastering for iTunes".
Last yeas I posted this topic: "Pandora-ready master? Please, help!
The most clear reply was from jackthebear
"Sorry to hear about your grief.....
There is no "radio ready" mastering for a specific station or band or internet or whatever......
Any ME who charges you the appropriate amount of shekels should furnish a master that will translate well across a broad range of playback systems and devices......the only caveat being if there's some kind of limitation in that system where it will not playback as you'd expect.....
Scott Hull demonstrated the exact same attitude back then. We talked on the phone for good 40 min or so - about nothing. I assume he didn't even know about AAC format Pandora was using. I'm actually pretty sure about it, because I tried to ask Scott about AAC several times.
Now bravo, Scott - no irony implied.
"A message from Scott Hull about Mastered for iTunes"
...The sales figures make clear that Apple's AAC format is currently the dominant format in the marketplace. CD sales continue to fall, and though vinyl has had a miraculous resurgence, it's a small fraction of the pie. Basically, music producers, labels, and artists are adjusting to the new reality on the ground, and have found that it's time to recognize that the market's dominant format -- AAC -- has unique mastering needs, just as CD, and tape, and vinyl did before.
Though there's some confusion in the press, Mastered for iTunes isn't just a promotional opportunity. The surge is being driven by Apple, but the concept would apply to any digital format, just as it did for analogue, optical, and ..."
That's how I learned some mastering techniques myself. And met a wonderful person and super-human-engineer Eric James Phibarnmastering.co.uk