So I just finished mixing this album and my clients have asked if I could master it for them.
As no one has yet addressed the mastering an
album aspect of this yet - which is an amportant part of this question - I'd like to add this nickel to the discourse:
I'd recommend as one method starting with the quietest song on the album. Not necessarily the quietest recorded level, but what seems to be the quietest, least energetic, least complexly-arranged and mixed song on the album. Get that sounding it's best and nudge the levels up with very light compression. Tom V. has given some great advice regarding the relation between EQ and compression, and as far as some general procedures for polishing the mix.
Don't expect to necessarily get that song up to commercial CD levels. You might get lucky, but the reality is probably by the time you get it that loud the mix will be quite brittle sounding and fatiguing to listen to. Just bring it slowly and *LISTEN CLOSELY* to the actual quality of sound. At some point it'll start breaking apart, probably before you would expect it to. Just bring it to that point and back off maybe a dB or two from that cliff edge. You (and they) may not be perfectly happy witht he volume, but trust me, if they are listening for any extended time on the road, they will be happier in the long run with a slightly quieter mix that they can actually listen to until they get back home than a loud one that their ears get tired of after two listens.
You now have a base by which you can judge the finish on the rest of the tracks of the album. Typically, if the songs are all recorded and mixed in the same locations, they will probably want to have a similar overall "timbre", even if the mixes and arrangements are quite different. Something to keep in mind as you're polishing the remaining tracks.
Also - and maybe more obviously - most folks will want songs to have a fairly constant volume level from track to track. As you have pushed the quietest song to it's max, you should in most cases be able get the rest of your tracks to a matching level without too much hassle. Don't judge this by your meters or your RMS measurements, however, as those change relative to the density of the song. Just simply fall back on your ears to pick an overall volume level that sounds pretty much the same as the first track regardless of what your meters tell you, and you'll have a good listening experience.
IMHO YMMV MADD RSVP MPG POTUS, etc.
G.