Here's a link to the subject on Wikipedia: DRM Overview

Here's what I know about it:

All CDs and digital files have some sort of meta data. Some more or less (older CDs obviously had a lot less since not much could be done with it). Anyway, it's data that is usually separate from the audio stream. For instnce there is basic stuff like track info, album timing and other helpful or "neutral" info having to do with the CD itself. So thus DRM should in theory be data not actually part of the music.

It works in conjunction with particular playback codecs, hardware and software so as to limit copying, certain kinds of playback, in the most extreme cases, what kind of hardware it can be played on.

Many years ago a certain "intrusive" DRM/anti copying software was built into CDs by at least one music company which I can't remember now. It had some sort of high frequency signal built in that was sort of a primitive version of today's meta data and DRM. Anyway, it would prevent ANALOGUE taping of the music on certain tape decks if you can believe that! Problem was, it wasn't actually outside the audio realm and caused all kinds of problems in the high frequency realm and it just was a screwed idea all around. I seem to remember Stereophile may have reported on this at the time (this was around 1988).

So companies have been trying all kinds of BS off and on for years, but it wasn't until the advent of rampant copying, MP3s and file sharing that things really took off. Then the varying media/music industry "enemies" came together for the mutual evil purpose of further screwing things up, which they are gradually starting to admit. Sort of...

So bottom line- today's DRM should NOT being affecting your sound, assuming it let's you play it.

Note, however, that DVD-A discs encoded with MLP use a watermarking scheme which *DOES* manipulate the sound. It's supposed to be inaudible, though.

"It's supposed to be inaudible, though."

Yeah- that's waht they all say, and later it usually comes out that it does in fact affect harmonics or some other aspect. DRM just sucks from beginning to end! Makes me happy every time I put on a record that I don't have to worry about it most of the time though.