Using buss compression, or any kind of processing across the entire two mix in Pro Tools, is a common and often mis-executed process.

Like most things, there are effective ways in doing this just as there are many self-defeating ways. Let's take a moment to focus on one of the preferred methods.

For this example, we're going to be looking at a small demo session that's using T-Racks 3 across the stereo mix. T-Racks 3 is a long overdue update to IK's classic T-Racks. Promoted as a mastering solution, the original T-Racks found it's way into many engineers DAWs for many applications other than mastering.

Now, the new version not only includes the original four processors (Compressor, Limiter, EQ, and Clipper), but also comes with a rack of new emulations that take the plug-in to a different level altogether.

In Pro Tools, there is often a temptation to apply the stereo processing of a mix to the Master Fader. Although this isn't exactly "wrong", there is certainly a more effective way of doing this. In case you didn't know, the inserts on a Master fader in Pro Tools are post-fader. This means that if a compressor plug-in is applied to the two mix on the Master fader, any volume automation of the Master fader that is intended for the two mix is going to be happening before the compressor in the signal chain, which might be wanting to turn everything back up. The way to avoid this is to create a sub-master fader (a stereo Aux track) and apply any needed two-mix processing to it. All the tracks in the session that we're routed to the main left and right outputs should be re-directed to the next available buss with the input of the new sub-master being set to the same. The sub-master is routed to the main outs, and the Master fader is only there for any necessary dither. Now, any volume moves on the two-mix can be done with the sub-master fader which comes after it's inserts in the signal chain.

The other important thing to note when using any kind of two-mix processing is the appropriate point during the mixing process to add it to the signal chain. Plug-ins make it really tempting to take a finished mix and apply a plug-in preset across the entire mix to make it louder or more exciting. While there are times this can be useful (like printing some mixes for a client to hear so they are a little louder, etc.) be warned that by doing this at the end of the mixing process as a "keeper" will more than likely change the sound of the mix. Rest assured, things like the level of the bass and vocals can shift dramatically. The way to avoid this is by introducing the two mix processing (compression, etc.) early on in the mixing stage and certainly before any automation is written. This way you can work with the two-mix processing and not have the it work against your mix. Volume moves and EQ tweaks can be made in context of what is happening across the two mix and yield a overall better sounding end product.

Buss compression can be a great thing that really tightens up a mix or totally destroys it's dynamics. When in doubt, you can always press the bypass button and compare.

A demo of T-Racks 3 can be downloaded here.