I often read recommendations to mix with compressors/limiters in the main bus so we can adjust to the effects of mastering during our mixing, and then to bypass those dynamics plug-ins when we export for mastering. Why not put in the full mastering chain and mix and master your track in one pass? I mixed my latest track with the following chain in the master bus: Cubase's full-band compressor with a 1.2:1 ratio for 4-5dB of reduction; Powercore EQsat plug-in with a broad four-octave dip of 1dB at 850Hz; Powercore Master 3X multi-band compressor plug-in operating at a 3.2:1 ratio with 2dB of gain reduction; and ToneBoosters' Barricade limiter set to a -1dBFS ceiling and showing 3-4dB gain reduction.
Damien McEwan, via email
SOS contributor Mike Senior replies: Using a compressor on the main mix bus during mixdown is indeed very common (although by no means universal) in order to 'glue' the mix together or create extra excitement via gain-pumping effects. Given that this bus-processing can impact quite heavily on the way you balance the track, it makes sense to have it working while you mix, particularly so that you can judge your effects levels and fader automation sensibly within context.
However, limiting the main output bus during mixdown is a whole different kettle of fish, because the main purpose of full-mix limiting is simply to boost the subjective loudness within the digital headroom. As such it's usually much faster-acting, and the goal is usually to make as little difference to the mix balance as possible. Furthermore, setting up a limiter for the best results is usually a delicate process, where small shifts of the input level and plug-in controls can make big differences to the sound. So on the basis that mastering limiting shouldn't normally affect mix balance, and that it adds to the already considerable complication of creating a decent mix, I usually recommend that this process be left until after mixdown.
Clearly there are some chart-oriented producers for whom the loudness of the master is an important primary concern. In that context having a preview of what the side-effects of heavy-handed loudness processing (including limiting) will do to the mix tone and balance can allow some pre-emptive compensatory steps to be taken by the mix engineer. However, even in that case, I'd favour bouncing your mix out to a separate project to experiment with this processing, even if that means that you then have to hop between the mix and a pseudo-mastering project. One reason I prefer working this way is that it puts fewer limitations on the mastering-style plug-ins I can use within my PC's available CPU resources, and usually makes it a lot simpler to switch between my own pseudo-mastered mix and a selection of commercial reference tracks — an essential process when judging the results of your own mastering. Also, from a psychological perspective, being unable to immediately enact changes on the mix during the comparison process encourages me to clarify my own thoughts on the deficiencies of my own production across my available monitoring systems, and I find that this means I go round the houses less often while finalising my mix settings.
Equalising your main output bus at mixdown is pretty common. It's very easy while you're working on a mix for your ears to get used to a skewed tonality (they're very good at adapting), and if this shows up during comparisons with commercial tracks then it's much easier to deal with using a decent-quality master-bus plug-in than by tweaking the individual EQ settings across dozens of individual tracks.
Multi-band compression, on the other hand, is another thing that I suggest leaving to a separate mastering stage. Again, this is because it's so fiddly to set up properly, and you're not normally looking for it to impact hugely on the mix tone or balance; the heavy multi-band compression of the late '90s hasn't aged well, and isn't very fashionable these days. Also, in my experience, it's very easy to take your eye off the ball as regards getting the mix balance right when there's a multi-band compressor in the master bus, because the compression can often counteract your mix settings and disguise subtler balance problems that need addressing. Or, to put it another way, it tempts to you think that the mix is easier than it is somehow, so you work less hard.