What Is Mix Bus Compression?
Mix bus compression is simply a compression technique where you put a compressor at the end of your signal flow, usually, the mix bus or the stereo output channel of your mix, and this compressor will compress the entire song together.
Since all the tracks are routed to the output of that channel, putting a compressor in the way makes the compressor react to all of the tracks that are going down your final stereo mix/master channel and out to your speakers.
Why Use Mix Bus Compression?
You use mix bus compression (and sometimes limiting) to glue your tracks together.
To me, gluing your tracks together means reducing the dynamic range slightly so that the loudest peaks and softest valleys are closer together and you can hear everything a little more clearly.
You don't want the levels of your mix to jump around too much so using mix bus compression will help steady the mix so that it sounds more "professional."
How To Use Mix Bus Compression
Add a compressor to your mix bus where all your tracks are eventually routed. I tend to add the mix bus compressor once I've got a rough static mix with both volume and panning to squeeze the mix together before I add any further processing to my groups, busses, or individual tracks. You want to mix your song into the compressor so adding it early in your workflow will be beneficial. Personally, I always mix into a limiter at the end of my channel, but I use mix
bus compression at the start of the mix bus to add glue. The limiter is only for catching stray peaks and letting me know when I've gone completely overboard and am mixing way too hot.
A VCA compressor is usually more transparent and very popular for this technique. The SSL Bus compressor is a VCA compressor their models are great if you don't want the compressor to unnecessarily color the sound of your song. Of course, try out a few compressor models to hear how they react to your tracks and decide from there.
Use a 2:1 ratio and aim for a couple of dBs of gain reduction with a medium attack and medium release. A fast release will kill the transients of your tracks and is mostly to blame for sucking the life out of your song. So if you've never been able to get mix bus compression to work, maybe it's because you've never tweaked the attack to let the energy of your tracks through.
You don't want the release too fast or too slow either because you want the compressor to breathe with the song. You want the song to move and your compressor should help, not hinder that movement. Often, the auto-release function is great because it will listen to everything that's going on in the song better than you can at any one point. I'd err on the faster side if you don't have an auto-release and want to avoid squashing. Time the release so that it feels
musical and even.
Tl;Dr:
- What? Mix bus compression helps you glue your tracks together to make your mix sound more professional and tight.
- Why? Reduce the dynamic range just slightly so that everything can be heard more clearly.
- How?
- Ratio: 2:1
- Threshold: Aim for 2 dBs of gain reduction
- Attack: Medium to slow
- Release: Fast to medium. Auto-release often works well.
- What kind: VCA compression models work well and are popular, but experiment to find your sound.
If you want to know more about how to use compression to get better mixes, I have an entire module dedicated to it inside my Mixing With 5 Plug-ins course here.