Challenges in Mastering a "Various Artists" collection...

[A NOOb question, fellas:]

One task in Mastering, as I understand it, is to create a similar frequency contour for all the songs on a particular album/CD, so the album has a certain coherence... a certain "sound" to it... as well as a good universal hardware playability... Correct so far?

I can understand this procedure going fairly smoothly when all the tracks have been recorded by a single artist.... and, most likely, in the same studio with the same cats playing on the track, etc...

In this event, I'd think finding a nice contour for all the tracks would be very do-able, no?

But what if you're mastering an album of-- let's just say--- 20 tracks, each of which is by a different artist, each track in a different style, with different musicians, different mixologies, different compressions, different audio fidelities, different EVERYTHING...

How would the skilled and savvy Mastering Engineer approach THIS kind of project...? What kind of frequency/loudness contour could satisfy the qualities of all such disparate tracks?

The way to master this is to make each track sound as good as it can sound, within the confines of the genre. There's a certain amount that you can't undo, though, since you're getting them already mixed and "mastered" by someone else.

Not much point in trying to match spectral balance with different material, just make sure that transitions aren't jarring and that levels are sensible. Don't make the solo singer with an acoustic guitar sound as huge as the 14 piece horn band.

Think of it as a variety show, not a collection of similar music (because it isn't).

A good friend asked me to put a bunch of his old 45's from his jukebox on to a CD for him. These are older tunes like Timothy, Summertime Blues, Beach Boys and Beatles, Beach Baby, Red Rubber Ball, just all over the map feel good stuff. I just ran them off to the same input into the computer. The volumes and mixes were just everywhere. May try to master that bunch one day. I guess radio compression kept stuff in bounds but there certainly didn't seem to be any rules to mastering back in those 50's to early 70's singles.

Run them through the "Normalize" and "Level Track" filters, and hope for the best.

If you want to use technology to help you set your relative levels -- use an analysis tool that lets you select a representative time slice of each track and compute a representative RMS average for each track (if you use the whole track, a quiet intro or long quiet section can throw off the average) as well as its peak level. (Sounforge Tools/Statistics can do that for you.)

From there you can derive a strategy. Either do no compression but find a set of levels across the collection that allows them all to have about the same RMS level without crashing 0 and make simple linear level adustments to bring them in line.

Or...

Apply some amount of peak limiting to allow you to do about the same but taking down any 'extreme' dynamic ranges that force the RMS for a given track down (vis a vis 0dBfs).

I believe this sort of project is the most demanding for an ME and proves or disproves their mastery over their craft.

What are they going to do... send each song back for a re-mix?

eB