Question on rendering a master mix

Once you've mixed a song to your liking and you render out a master mix, I assume that means the song is ready to send to a mastering engineer for mastering, correct? Or does it mean that you have mastered the song and it is done? For instance, I have mixed a song. Should I bring the entire project file to the Mastering Engineer and let the ME do the render, or do I just bring him the bounced stereo (or mono) file?

It could mean you're finished in a perfect scenario. :) It means you have a mix finished as well as possible and as "right" as possible. (And just like the advice during recording is to NOT say "We'll fix that in the mix." if some challenge comes up, don't leave an unfinished mix to "fix in mastering".) Mastering is putting a final mix into consumer delivery formats intact. For an album of songs, there might be an additional step of adjusting the overall level of the songs to present all the mixes at the same volume. If you feel your mix is finished, hand that to your mastering engineer. If you don't feel like the mixes are right and were looking for them to get some magic from 'mastering', give them your mix in progress to finish instead. It's much easier to finish a mix from the multitracks than pulling and tugging on an unfinished mix. Asides: Mastering CAN get into restoration work on a mix where the multitrack masters were lost before a final mix was made. Sometimes in the "fast paced industry" unfinished mixes are in fact handed to the mastering engineer. (Sometimes that 2nd pair of ears gets the quick and dirty job done quicker than giving the mixing engineer time to finish properly. And it's pop music no one really cares about anyway.) The version of the master made for portable devices (iThings) is often limited and boosted and brightened with eq vs. the 'proper' full quality final master. This leads to a lot of confusion among those who have only ever heard this (eg. someone with an mp3 collection). "Why are my mixes too quiet?" They're not actually! You're listening to volume war hyped stuff that has been boosted after the fact. The visual analogy would be a small shrunk down icon image. The image isn't created at icon size on the artists "mixing board". It's created at full size and shrunk down to icon size in a 2nd step.

I take the definition of mastering to be to make a song/album/ep 'suitable for distribution'. It depends on the intended audience/destination for your music. If it was simply for your own listening pleasure then you may be perfectly happy with your mix + a limiter on the master to ensure it doesn't go over 0dB. If you intend it to be heard by others then using an ME is the way to go (unless you have great mastering chops yourself). Most mastering engineers will simply want the stereo bounce of your mix. Render it out in the same quality you mixed it at. No need to upsample to 96 kHz if you were working at 44.1/48 kHz for example.