As both a guy who makes music and a guy who masters other peopleâ€™s Iâ€™ve encountered the tendency â€“ sometimes even in myself â€“ to write off some mix errors as just â€œstuff that can be fixed in mastering.â€
While maybe itâ€™s true that the mastering engineer *can* indeed fix these things, the smartest policy is to fix these things in the mixing stage first. Any fix in the mastering stage comes with a cost, whether that cost is monetary (extra engineering time means extra $$$) or just the cost to the overall quality of the track. That kick drum too boxy in the 200hz range? The mastering engineer could do a very precise reduction on that frequencyâ€¦but anything else with harmonics at that frequency would also be affected. Vocals need to be louder? A little middle-band compression may help tighten that up, but at the expense of the overall width of the track. It may be subtle, but itâ€™s going to hurt.
Iâ€™ve often heard of mastering referred to as a â€œsurgicalâ€ process. That may be true to a point, because the tools are usually precise, specific, and often dangerous for the unpracticed to play around with. The analogy sort of breaks down at that point.
A better analogy would be perhaps one of a car detailer. The guyâ€™s got special tools â€“ an orbital buffer, polishes, hammers for pounding out dings, stuff that an average car owner probably doesnâ€™t keep handy. The detailerâ€™s job is to make your car look as good as it possibly can, buff it to a high gloss, maybe smooth out some scratches and chips. But you wouldnâ€™t ask the guy who details your car to fix a problem with your head gasket or your muffler. The mastering engineer is like the detailer â€“ heâ€™s got the tools to make your track shiny, polished, and professional-sounding. And while he may have the ability just by chance to fix a mix problem (much as the detailer probably knows how to change your oil) itâ€™s not the sort of thing you really want him to be doing.
Itâ€™ll save you, the artist or producer, time, money and headaches to address any mix problems at the mixing stage, and not the mastering stage.
So what about the case where the engineer hears a problem you missed? A good mastering engineer would likely tell you about it. In the world of the radio-hit machine, maybe not, because it has to be done yesterday and ready for the radio, but there it doesnâ€™t come up as much to begin with because your track is mixed by Mark Stent or Tony Maserati and itâ€™s just not an issue. For the rest of the indie pro-sumer crowd, though, the option is usually there to send the engineer a new mix with the fixes in place, and any resulting charge will be minimal, if thereâ€™s any charge at all. I know that when I master an album, I listen to it first so I know what Iâ€™m going to do before diving in, and Iâ€™ve on more than one occasion said â€œhey, the bass is a little loud on track 3â€ or â€œthat lead synth has some weird phasing, is that intentional?â€ and if itâ€™s a problem and not an artistic decision, Iâ€™ll gladly take delivery of a new mixdown before I start mastering (there are limits, of course â€“ eventually Iâ€™ll want to get to mastering and not waiting for the 8th upload of a new mix, and sometimes the engineer does have the right to say â€œlook, I donâ€™t know how to fix it or I just donâ€™t want to â€“ do what you can with it.â€ But these are rare cases).
In short, the strongest recommendation I can make to anyone about to submit their music for mastering is â€œgive them the best mix you can, and donâ€™t expect the mastering engineer to fix what you didnâ€™t.â€ A strong mix will need less processing in the mastering stage, leading to a cleaner, better-sounding master and a better experience for the listener.