SonicExplorer

35mm
Export your mix first as a stereo wav. Then import that into a new project and add your mastering chain, dither and export. That's the best way.

That's similar to the classic analog methodology, so to speak.  Is that approach still necessary now days with DAW's ? .... What would be the advantage of mixing out the song when you could simply put the tools on the final output bus inside the project?  

I started out in the analogue days, but that isn't why I use this methodology. There are no rules, but splitting the process gives you more flexibility and headspace - if you master in the mix, the temptation is to adjust the mix while you master and you will end up adjusting one to compensate for the other. 
 
By exporting the mix first, you have a copy of that mix forevermore. You can then remaster at some point in the future if you need to, or you can do multiple masters for different media from one mix - e.g. a master for mp3/cd, Spotify, vinal, radio etc.
 
As others have already mentioned, this method also enables you to mix a batch such as an album by importing all your mixes, laying them out in order, pre-mastering each track to get them consistent, then applying overall mastering for whatever media you are going to.
 
When I am about 2/3 through a mix I usually add some mastering plugs on the master channel (a bit of compression and limiter usually) to get an idea what the mix will be like once mastered. That's also good for rendering rough/preview mixes. Then I bypass the mastering plugs and make sure there is enough headroom on the master meter for the mastering process before I export the mix.

There are a lot of good points here.  One thing I have noticed when I mix and master:  as soon as I put the limiter in the signal chain, no matter which method, the sound always changes.  Typically it's the mids and vocals that change the most, tone and volume.  I work mostly with hip hop, so high levels are important.
 
So lately, I've been adding mastering processing to a submix buss before the master buss, and it seems to make the entire process faster and more inclusive.  I know that's not the traditional way so don't bash me.  However, cpu performance is my limiting factor here and sometimes I can get myself into trouble with so much processing on the master buss.  Also, this is typically for single song projects and not an entire album.  As others have said, final mastering for a commercial album release has other considerations you can't do with a single song.
 
 

Tho many engineers "mix into" the two buss w/ comp/limiters and even DQ, they still send it off to mastering (or do it themselves for us home types).  As said above, two different processes that still hold from the tape/vinyl days.

Bristol_Jonesey
Another approach with a surprisingly wide-held support is to actually mix right "into" your mastering chain from the very outset.
 
Admittedly  there are probably as many critics of this method as there are supporters - but it's worth trying out

I think this is super rare.  Having both Mastering Grade Compression + EQ (liner phase) along with a final limiter is very taxing on a system along with the full mix and other effect on tracks and buses.
 
Mixing into a bus compressor and things like that is common, but it isn't' the same as really mixing into a full mastering chain isn't super common in the professional realm.  

On a related note, I'll put a CD together when it all sounds good, burn a copy and play in my car...and without fail I'm fiddling with the volume knob from song to song--even though each song has used pretty much the same mastering plugins and is limited to -6dB.  
 
How do I get these songs to sound at the same appropriate volume after printing.  My ears aren't getting it done.  I assume there's some kind of "metering plugin" that I'm missing?

Thanks guys for the many replies and helpful insight, all great points.
 
Here's an idea I thought of, what do you think of this approach ?.....  (Disclaimer, I understand this isn't optimal for a body of art comprised of multiple songs, it would be more applicable for individual song releases):
 
1) Mix a project and export to WAV
2) Within the same project create another track (label it, say, Mastering Track) and point it at the mixed WAV file (not physically importing it into the project, just pointing at it).
3) Use the Mastering Track FX bin to add tools and master.
4) Highlight just that track and export to create a mastered file.
 
With this approach you can easily swap back and forth to listen between the mastered track and the mix tracks all within the project.  And if you make changes to the mix, they are automatically picked up by the Mastering Track since it is always pointing to the mix file name.  This approach also allows for better CPU management if that ever becomes a constraint.
 
Thoughts ??    
 
Sonic

jerrypettit
On a related note, I'll put a CD together when it all sounds good, burn a copy and play in my car...and without fail I'm fiddling with the volume knob from song to song--even though each song has used pretty much the same mastering plugins and is limited to -6dB.

How do I get these songs to sound at the same appropriate volume after printing. My ears aren't getting it done. I assume there's some kind of "metering plugin" that I'm missing?

you might have to master them keeping track of the RMS level rather than the peak level. RMS levels of a mastered track usually ranges from -12 to -8db. Anything above that is too loud, though a track can sporadisporadically go above that in certain parts.

SonicExplorer
Thanks guys for the many replies and helpful insight, all great points.
 
Here's an idea I thought of, what do you think of this approach ?.....  (Disclaimer, I understand this isn't optimal for a body of art comprised of multiple songs, it would be more applicable for individual song releases):
 
1) Mix a project and export to WAV
2) Within the same project create another track (label it, say, Mastering Track) and point it at the mixed WAV file (not physically importing it into the project, just pointing at it).
3) Use the Mastering Track FX bin to add tools and master.
4) Highlight just that track and export to create a mastered file.
 
With this approach you can easily swap back and forth to listen between the mastered track and the mix tracks all within the project.  And if you make changes to the mix, they are automatically picked up by the Mastering Track since it is always pointing to the mix file name.  This approach also allows for better CPU management if that ever becomes a constraint.
 
Thoughts ??    
 
Sonic

Like I said above, there are no rules. You can do what you like, but I think you are kind of making things more difficult than they need to be by doing what you propose in the long run. If you are happy doing it however you want to do it, then do it that way, but you asked for advice, and people with long-term experience advised you on the best method to use. They didn't advise that method because it was how things were done in the analogue days, but because they have learned how to best organise things for efficiency and recoverability in the future. The way the majority of people have prescribed is the best method for productivity and future compatibility. You can use another method, but you may find somewhere down the line that you run into problems, and then you will think, "Ah, that's why they said to do it that way!" 

I have mastered many albums including my own music.  I feel that mixing and mastering should not happen at the same time or mastering after a mix is not smart either because your ears are tired from mixing and generally you won't make good mastering decisions.
 
I like to mix and not very loud either. e.g. a -14 or -20 db rms mix.  It's OK to mix into some compression but make it light duties only. e.g. low ratio e.g. 1.5:1 and 2 to 3 dB of GR max.
 
Print the mix onto a CD and listen to it for a week here and there.  In your car, etc.  While eating dinner even.  You will find a bunch of things over the week that you will want to change.  You will start hearing things that are too loud and too soft etc.  Some entrances will be too loud or soft etc..   Make the mix changes at some point.  
 
Leave it again before mastering.  Another week even.  Then just create a mastering session which will be a stereo track with the three basic processors on it e.g. EQ, compression, limiting etc.  By leaving it you will hear it fresh again and make good mastering decisions.  Master after a good nights sleep in the morning as well. 
 
Use reference tracks while you are mixing and mastering as well. Good mastering requires no real vicious approaches to EQ and compression and limiting.  The mix should be so good that the overall EQ will hardly be required. Same with the compressor and limiter.  Don't master too loud.  It is not the go these days. 

To the post regarding uneven levels song to song. This is why you should use a Wave editor because they have the tools to do this. 
Here's an example of a wave editor ( acoustica 7)  analyzing a song. No guess work involved here.
https://acondigital.com/products/acoustica-audio-editor/  Try the demo, 
Note this song is a backing track and split Bass left/  Drums, keys right so therefore uneven. 

 
 
To the OP, You idea is creative but overly complicated. And your not going to hear changes to a mix until you re-export the song. 
 
What I do is export the mix., keep Sonar open
Open the file in the Wave editor and Analyze it. 
This information is critical and each song needs the be very close to the same readings. 
Even if it's a one off, I keep to my standards
I also top and tail another important task, 
I often find something is not perfect so I return to Sonar, fix that and re export. Once the check list of requirements is met with the analyzing I burn a CD and like Jeff so wisely has said, live with it for while making notes as you listen to the album everywhere possible. 
 
I will admit that one thing that has sped up the process is using the Brickwall limiter on my Master buss. I have it set to -0.40 as you can see above, it works.