by Josh Reynolds
Let's talk mix compression. I'm noticing a common trend in mixing that is moving away from compression in the traditional sense. Maybe your mix buss and the way you drive into it is perfectly giving an overall tone and dimension to your mix, and that's great! However, if you are looking for a more flexible way to create some movement and space in your mix, read on!
One common way to use compressor is to make something relatively louder. Reducing the dynamic range and then making that reduced gain up is one way to use a compressor. Often on individual channels that is what we are looking for, a controlled automation of the level of a track that makes it more consistent. The compressor makes that instrument stay within a certain dynamic to serve a purpose in the song. A lot of traditional dynamics processor designs were created to get the level of a program louder or more consistent without over-driving a device like a broadcast transmitter. However, these days we have more precise ways of controlling elements within a mix, like using clip gain across a track to keep the level consistent while leaving tone and harmonics to be managed separately.
Using a compressor on a full mix can also be useful. This will have an overall effect of "pumping" the entire mix down when one of the loudest sounds happens, recovering to unity gain ideally in time with the feel of the song. Of course, in this configuration we might be applying pumping to sounds that we would rather stay more consistent.
Sidechain it Up!
Another way of accomplishing this effect would be to only apply that pumping movement to specific elements in the mix. Instead of one compressor on the whole mix pumping down when the kick and snare drive into it (and at the same time further compressing our drum transients?!), we could apply compressors on busses of the bass, guitars, keys or other instruments. Each of those compressors receive a sidechain mix of whatever they should be dancing around.
I will often use an aux send from the kick drum to these sidechains, but you could create any combination of voices that you want the instrumental arrangement to make space for. This also allows us to set the final placement of the vocals to not be affected by the pumping between the drums and the rest of the instrumental. I will manually write automation for instruments to move a little around the vocal and use the sidechain to move instruments a little around the drums.
I like to use the Fabfilter Pro-C2 for this task, with attack and release times calculated for the tempo and feel of the track. Any bus compressor with a sidechain input could be used. Gain reduction might hit anywhere from -3 to -8 when the kick hits to get it to feel right. Usually either 2:1 or 4:1 ratio works well.
I use an app called musicMath to put in the tempo and make decisions about attack and release times. Release times that feel good are usually between 1/8 and 1/32 notes, but this is totally dependent on the specific tempo and feel. Maybe it's a 1/8 triplet, and maybe it's variable for different groups of sounds. Sometimes it's useful to have some groups of sounds recover from the gain reduction faster than others, for instance the bass might come back up on an 1/16th note timing while the guitars recover on an 1/8th note. Attack times are much quicker, if the release is 211ms, I'll make the attack .21ms as a starting point. Play with some times and see what feels good.
These techniques can produce a very consistent drum and vocal presence, with the bass and other instruments moving slightly in and out around the kick when it punches in, clearing momentary space for the kick while letting the other voices sit up a little more in between. If overdone, your track can get end up feeling too flattened out, but with just the right amount of movement it can help the mix breathe and have some motion in specific places where you want it.
Once you have the mix working the way you want it to, then maybe your mix buss compressor has some harmonic impact that you still want to make use of without actually compressing! Or maybe there was an overall tone you used to like and now don't need? There are no rules!
Happy mixing! I'd love to hear how your mixing techniques are evolving over time, hit me up at www.jreymix.com