There's been a bit of hype over the new re-mastering of the Beatles music catalogue, for a new set of CD releases and a Beatles version of Rock Band coming in September. The press release says that Apple Corps. (the Beatles record companies) are:
...delighted to announce the release of the original Beatles catalogue, which has been digitally re-mastered for the first time...
(My emphasis.) That's a marketing lie. The catalogue was digitally re-mastered in 1987 for the first CD releases. It had to be. You can't make a CD (or any other digital music medium) out of analogue audio without digitally re-mastering it first. Unless EMI and Apple Corps. consider the 1987 occasion the "first digital master" and the new ones the "first digital RE-master," which is a "that depends on what your definition of 'is' is" kind of semantic distinction.
Mastering is the phase of audio production where you prepare audio files for their final medium. In the days of LPs, mastering engineers evened out the levels of different songs so their average volume didn't vary too widely, then applied various types of equalization to the master tapes, designed for the way record players were manufactured, and to prevent heavy bass frequencies from causing the needle to hop out of the grooves. Setting standards for those masters were one of the things the Recording Industry Association of America used to do before it turned to suing its customers for file sharing.
There would need to be different masters for cassettes or eight-track tapes, by the way.
Engineers mastering for CDs didn't have to worry about the groove hopping, but for music recorded on analogue equipment (i.e. tape machines), they did have to digitize it into ones and zeroes using what's known as an A/D (analogue-to-digital) converter, as well as still making sure the various songs were of comparable average volume. That's the digital re-master.
These days pretty much everything is recorded digitally, either directly in a computer or by digitizing signals from microphones and guitar cables right at the source, so for new recordings the digital master is the first one. Re-mastering might be done later to make it sound different—or, with a bit of irony, to convert it to analogue for special LP pressings or DJ vinyl singles. That would be an analogue re-master.
So it's true that these new Beatles CDs (and, with luck, eventually iTunes tracks) will be new digital re-masters, but they won't be the first ones. If you already have a complete collection of Beatles CDs from those 1987 digital re-masters, these new ones will probably sound different, maybe better. But they could sound worse.
The trend in the past decade has been to master or re-master pop recordings to sound way too loud, and to crush all the dynamics (the difference between the loud and soft parts) out of songs. That's why listening to a top-hits radio station, or a playlist of current top pop hits, can actually be physically exhausting. Your ears never get a break. It's called the Loudness Wars, and we've talked about it a lot at my Inside Home Recording podcast. While it has seen a bit of a backlash recently, the risk is that EMI's engineers might have succumbed to the trend.
It happened a few years ago, when Genesis released re-mixed and re-mastered versions of many of their albums (even in surround sound). The audio compression wasn't especially extreme, and the re-mastering was useful for some very early recordings and bootlegs with poor sound quality, but many of the band's well-known albums from the '70s and '80s sounded too modernized—and, for die-hard fans, simply wrong, almost like cover-band versions of the tracks, or the "Greedo shoots first" special editions of the Star Wars movies.
I haven't heard the Beatles results yet, but I find it encouraging that EMI has also gone to the trouble of making new mono re-masters of the Beatles catalogue as part of the current set. If they're willing to be that retro, I suspect they've probably avoided over-compressing the stereo mixes too. I sure hope so.