MASTERING VS. MIXING
You will find about 10,000 posts and you tubes on this with as many definitions.
Mixing and mastering are two completely different professional fields, and when people are making records for labels, they use separate "mixers" and "masterers." They are specialty fields in the pro world. Home recorders have to be both.
A mix basically refers to how the levels of the instrument are set on the board (in a DAW on a real board) and when and how those levels come up and down with faders, and how they are panned. Mixing also involves some basic application of effects such as eq and reverb.
A "Master" focuses on the exact
sound of the final production and gets into areas like "spectrum analysis" and "dynamic range" and volume, and many, many subtle tweaks designed to make the mix thump or sparkle.
There are many, many ways to attack this--and it gets confusing.
Some people enter the mastering phase before the bed and vocals or instrument sections bed are rendered, just after levels and fading cues have been set (the mix.) *
* There is a lot of semantic cross-talk on this in the field. In the video by Graham posted above (a great video) by the way, he talks about the importance of getting each track to sound great before you move on to the master, and he describes that as part of the mixing process. Whereas, in his description, the master is more of a process of making sure tonal color and volume are the same on all finished musical tracks (i.e., songs) on a CD or collection. However, other people describe "mixing" as setting levels on faders, panning and basic eq. The level of detail Graham is describing as "mixing" is sometimes done by people who would say they are mastering. This is what makes it confusing.
At any rate, the point is this: if you want to add more mid-range or warmth to JUST the acoustic guitar, and it is already in the mix you hand to a mastering engineer, there is nothing you can do. The cream is already in the sauce so to speak. Anything you do will affect the entire bed.
So some people like to have their hand in mastering each track, and also mastering the final. But "mastering" involves the precise SOUND whereas mixing involves the LEVELS--short version of it all.
I love Ozone 5 as a mastering tool (one of many) but I am growing somewhat disenchanted with using tools like Ozone 6 as a one stop shop for final masters. They just seem to make things too watery and brittle for my ears.
Dynamic range is the key to great music, and you can't beat the old TT DR meter for keeping you honest on that.
You want the acoustic to sound like an acoustic, and the bass to sound like a bass, and you want to make sure things are panned, but not panned too much. If you get a great EQ on individual tracks, the mix will sound warm and you will need very little mastering effects after the fact though you may choose to use some to add some extra sparkle or kick or "ooomppfff."
But, if you you don't get a great EQ and sound and mix on individual tracks before you start to use mastering software, no setting in the world will be able to help you. Hope that makes sense.
Just get a good dynamic range meter and make sure you are in the 9-12 range (or higher for classical) and you'll be good.
Also leave some headroom, about 1 db. Don't max it out.
Here is a picture of my famous buddy Yoram Vazan (friend to countless hip hop pioneers) at his board. He is known as one of the best "masterers" in the world now. He helped me with some of my early stuff at the now legendary Firehouse Studios in Brooklyn.