I’ve been experimenting with mix‑bus compression, and quite like the glue and punch that it can offer. But at what point in the mixdown process do you think it’s best to engage the master‑bus compressor?
SOS Contributor Mike Senior replies:The main difficulty here is that there are two conflicting factors at play. First, inserting a compressor over your master bus will inevitably change your mix balance to some extent. For instance, it’ll frequently boost low‑level details such as instrument sustain tails and reverb/delay effects, and it might also cause strong drum hits and bass notes to duck lower‑level signals. The earlier in the mix process that you fire up your master‑bus compressor, the sooner you can start adapting your mix settings in response to these balance changes. Then there’s the fact that the operation of a master‑bus compressor will depend on what you’re feeding it with, and it’s thus difficult to assess the suitability of your compression settings if you’re feeding it with a mix that’s incomplete. In other words, the later in the mix process you add the master‑bus compression, the more effectively you’ll be able to set up that compressor.
So for every mix you do, you’ll have to make a judgement call that weighs up those two competing factors in relation to the unique demands of the music you’re working on. For example, with an acoustic jazz track I might apply my master‑bus compression right at the end, on the basis that the very gentle, low‑ratio setting I’d be planning to use wouldn’t appreciably impact any of the musical balances between the instruments, and all I might have to do is tweak my reverb return levels a little. But then with a heavy rock track, where I want to use ostentatious level‑pumping compression on the master bus, I might introduce that master‑bus processing quite early on in the mix, when I’ve built only the most basic skeleton of a dry rhythm‑section sound — simply because I know it’ll be pointless trying to judge the balance of any of the other tracks outside the context of that level‑pumping. In that scenario, though, I’d probably have to revisit the master‑bus compressor settings several times throughout the mixing process as the full mix sound developed.
It’s important to realise that the mix and the master‑bus compressor interact, so you can’t compartmentalise the two things.
It’s important to realise that the mix and the master‑bus compressor interact, so you can’t compartmentalise the two things. The earlier you introduce the master‑bus compression, the more time you’ll likely have to spend fiddling around with the exact compressor configuration and settings; the later you introduce the master‑bus compression, the more you’ll likely have to adapt your mix settings in response.
In practical terms, what this means is that I’ll normally introduce more dramatic master‑bus compressor settings earlier in the mixing process, while leaving subtler ones until later. And this same rule of thumb carries over to other types of master‑bus processing too. If I were multiband‑compressing my master bus, for instance, I’d only ever be doing so for subtle detail enhancement, so it would make much more sense for me to add that late in the mix process. With things like tape emulation or tube saturation or anything similarly ‘colouristic’, I would normally only apply that quite subtly, so again I’d add that close to the end of the mix. However, on those few occasions where I’ve been deliberately mixing into some kind of character processing for a specific vintage/retro/lo‑fi sound then I’ve sometimes inserted those plug‑ins pretty much from the get‑go, even though I may have literally only a couple of instruments in the mix.