In short, mastering is the creation of the production master. The "final destination" of all the files, assembled to a compliant format from which all "on the shelf" copies will be made.

"Way back when" the whole point of the process was to affect the audio as little as possible while creating that production master. Over the last couple decades, it's "grown" to some extent to be the "handshake" between the production process and the replication process. The mastering engineer is generally charged with taking the original mixes and "tweaking" them into sounding like they all belong on the same record. Creating a master with a cohesive sound that has the right "flow" to fit the mixes.

A lot of people mistakenly think that mastering is al about "making it really loud" -- While the mastering phase is the "right time" for such things, it's pretty low on the list of priorities. The first is to bring out the best qualities and minimize the worst qualities of the recordings. Getting them "loud" is an afterthought.

The general tools are compression and equalization. A "normal" (for lack of a better term) chain may consist of a collection of transparent and colored EQ's, compressors and converters. Perhaps the odd limiter here or there.

Occasionally, more "radical" tools may be employed -- De-essing, multi-band (a.k.a. "maul-the-band") compression, noise reduction units, pop, click, hum removal, etc.

Every mix asks for whatever it needs. To get a collection of mixes to sound cohesive, the dynamic range of each mix is adjusted to fit in with the rest - Or perhaps just the one before it - or after it - or both - What's good for a particular mix might not be the best thing for the project. It's a holistic approach, but at the micro-level.

Good question - A lot of people think that it's because the mastering engineer wants to "take credit" for volume (and the misconception leads a lot of people to think that mastering is only about volume).

But the truth, of course, is something completely different -- The reason that nothing should be done for the sake of volume is that it can limit (no pun intended) what the mastering engineer can do during the session. For example - A steady state noise which might be very easy to minimize while it is a steady-state noise might be nearly impossible to attack if the overall levels in the mix are fluctuating. Sibilance (which should really be taken care of in the mix anyway) can go from a simple nuisance that might be lessened considerably can "flat-top" into uncorrectable distortion, making any effort during the mastering phase more or less futile.

If you want to hear how your mix might handle the eventual "abuse" during the mastering phase, then by all means, throw a limiter on it and squash it to mush. It can actually be an ear-opening experience, as some elements that may have gone under the radar are obvious and obnoxious.

Fix those things and try it again. But make sure the rendered files sent to the mastering facility don't have that limiter in place.

A little buss compression is an entirely different thing -- Mixing into a buss compressor (not the same as adding it later, which can very easily lead to over-compression) can be just what a mix needs to "glue it together" somewhat. A dB or two can make a fairly dramatic difference. But again, don't overdo it - If the mix is asking for more than a dB or two, find out what is too dynamic in the mix before subjecting the whole mix to compression it might very well not need.

I can see why it could be confusing occasionally... I've seen some places that have "one pass" and "two pass" - - Even three pass mastering. I have no idea what it means. I guess they do an "okay" job with "one pass" and then a "nice" job with "two pass" and then a "really good" job with "three pass."

That freaks me out. We've called "one pass" mastering "one pass" mastering for a long time now. So to do away with any confusion:

ONE PASS MASTERING - At MASSIVE Mastering means:

Treating the entire recording as a single track.

Let me explain why you'd want to do something so odd...

Live recordings -- Orchestral, usually -- You make a recording of a concert and nothing changes from piece to piece. Or certain live-tracked "jam session" recordings where the tracking settings are made, the band does their thing, and then the same for the mixes. You wind up with a very consistent sound from track to track that can be processed with a single "global" setting.

During the mastering session, at the client's request, "one pass" mastering would entail finding a single setting that works for the entire recording and then process it in one pass from start to finish. It's not "corner cutting" -- It's not an "okay" job -- It's treating a very consistent recording very consistently.

Why does it cost less? Well, it takes less time to document 10 recall sheets than it does for one. It takes less time to process a collection of tracks if they're all using the same settings on the same gear.

"One Pass" mastering is NOT "I'll use the good gear on the next pass" -- And it's not for every project. It's very rare that it's used, very rare that it's asked for. But it's certainly a valid option for some projects.

This is also a source of much confusion -- Many people would almost reflexively answer "the cheetah." And while the cheetah's 70 MPH bursts of speed are certainly impressive for any land animal, the Peregrine Falcon has been clocked at speeds in excess of 230 MPH in a downward swoop while chasing prey.

What does that have to do with mastering?

Nothing! I just thought it was cool. Hey, you do what you want on your blog. :-)