Mixing & Mastering
Soundtrack Music and Songs
The mixing process extends to this, but mastering takes a broader view—you’re focusing more on each individual track when you’re mixing. Mastering focuses on idiosyncrasies in each track with an eye and an ear toward their progression. It takes in all the tracks as a whole.
Basically, mixing is the step before mastering that involves adjusting and combining individual tracks together to form a stereo audio file after mixdown. The stereo file is then mastered, which ensures that the various songs are clearly polished and form a cohesive whole on an album.
Sound Design, Mixing and Mastering for Film
Film audio isn’t mastered as such, in the way that music is. Dynamic range is still important in film audio and adding compression may bring up the noise floor as well as increasing the level of recorded background sound.
Most important of all, is to mix it in a properly treated space on decent monitors, I’ve seen too many student films where the guy has mixed the sound on his Macbook using only the built in speakers for referencing and then gets a nasty shock when it’s played back on a decent system.
As far as general advice goes, like music, the voice is king, people need to hear what is being said more than anything else. Bad sound is what is most likely to give the game away, worse even than poor acting or clunky editing. Clipped recordings, too much background noise, inexpert fades, disparity in levels between scenes. Reference between scenes to keep your levels right, leave plenty of headroom (film audio RMS levels being WAY lower than most modern music), make your transitions as seamless and as well-synced as possible and clean up any less than ideal audio. Izotope RX is great for this, version 2 especially.