Firstly I'm not here to tell you what to do or what not to do. There are so many things you can do with audio and like most things there are no rules, all I (and others) can do is explain what results you can get by following a certain path, it's then down to yourself to decide what to do with that knowledge and how you want to use it. Finally it may be worth noting that I'm speaking of somebody who both masters other musicians tracks as well as producing my own.
Why put FX on the Master Buss?
- It can makes things sounds louder / more aggressive
- It can make things sound more cohesive (think ssl style compression)
- It can make things sound clearer / weightier
- It may give a unique sound (maybe reverb for a far-off / dreamlike style sound)
Why not put FX on the Master Buss?
- It makes it harder to tell exactly what's going on in the mix
When you have FX that are designed to saturate / distort the sound of the mix or 'glue' things together. It can make it much harder to hear exactly what is happening in the mix and because of that you may miss something. I guess the beer goggles example is fitting here. It's like if you're out on the pull, yes the alcohol is going to make the whole social interaction a lot more fun and easier but it's going to make it a damn sight harder to tell which girl to bring home
- It can steer the mixing process in an unnatural way
Okay so you have the drums and bass in the mix. Things are sounding good but a bit dull. Nevermind whack the high end up on the master buss and everything is balanced again right? Well yes but what happens when you bring in the next sound which is now too bright so you have to EQ that out, now the hats are too bright in the mix as well so those have got to be EQ'd to compensate. An initial problem which could have been fixed earlier in the chain (EQ'ing the drums and bass) has now escalated into a global issue of everything being too bright. It's better to fix these things earlier on to give you more flexibility.
- It makes things sound better than they actually are
It's great that putting saturation or similar on the master buss will make things sound edgier but it may take away from processing individual channels because of it. The reason this can be bad is that you are more likely to get a 'harder' sound if you build up the loudness from the word go. So get a kick that sound good mix it with a good sounding snare which you've processed. Maybe Get some processing on the drum buss as well so that by the time you even get to the master buss you have something sounding great. The master buss in this instance is just adding that final layer of 'goodness'
Final Thoughts
Just to sum up my thoughts on using master buss processing. If all is sounding loud, clear and coherent then using master processing is great for bringing another layer to a great mix. The more that can be done in the mix to improve the sound though the better. If you do want to add something on the master buss then fair enough no ones going to stop you but just stop and think for a second, 'is there anything I can do in the mix instead to improve the sound instead?'
