12.1 Influence

Open arrangements might seem easy to mix at first. Take for instance a pop song with just a kick, a short bass note and the vocals playing on the beat, and all the additional elements only on the offbeat. In an arrangement like this, the lows get plenty of room and they won’t easily get in the way of other things. But if you think you can easily make this mix sound impressive, you could be in for a disappointment. Low frequencies mainly seem impressive when they affect other elements, like a thundering explosion that drowns out everything else. A perfectly defined mix that lacks this kind of drowning out sounds weak. But turning the lows all the way up is usually not an option in a studio production, as this only works when you play the mix at thunder level. The mix should still be impressive at a low volume, so another solution is needed.

The drowning-out effect can also be created artificially with compression. If you send the bass instruments relatively loudly into a bus compressor that’s on the entire mix, the compressor will mostly respond to the lows. This way, the entire mix is pushed back at the moments when there’s a lot of low-end energy. And if you don’t set the attack too fast, the initial punch of the lows will still be allowed through. The trademark EDM sidechaining of the kick drum takes this to the extreme. The kick triggers the sidechain of an extreme compressor, which is applied to all the other elements in the mix. This way, it ducks the entire mix, while the kick itself stays intact. As a result, it will even seem relentlessly loud on laptop speakers.

A compressor will always be a device that makes loud things softer, whether you put it on individual sounds or on an entire mix. The main difference is in the interaction between sounds that results from running them through a compressor as a whole. The sound that makes the compressor work the hardest also compresses all the other sounds in the mix. Especially in music that’s composed of isolated elements, this method can make it sound more like a whole. An orchestra that’s recorded live rarely needs such a treatment, because the acoustics and crosstalk already provide enough cohesion between individual parts. But if you’re working with orchestra sections or individually recorded samples, bus compression can make the resulting mix sound more like one orchestra playing together. In a lot of pop music, this type of compression has partly taken over the role of reverb and acoustics: the softer and longer sounds almost seem like reverberations of the rhythmic and loud sounds, due to the fact that the compressor mainly brings them out between the loud notes. So just like reverb, bus compression can serve as the glue that holds sounds together (see Figure 12.1).

Figure 12.1The vocals (red wave) and guitar (green wave) don’t blend well. They’re either too weak (A) or too dominant (B). If you use a bus compressor that mainly affects the vocals (because they’re relatively loud at the input), you can make the guitar relatively weaker when the vocalist is singing, and let it come back up at the moments in between—while simultaneously controlling the overall dynamics (C).

Border Patrol

Besides as glue for your mix, a bus compressor can also be very interesting as an indicator. You can see the compressor as a kind of soft ceiling, guarding the borders of your mix. When you’re struggling with mix balances and find yourself going down that treacherous road where you’re only making everything louder, it can function as a counterbalance. It forces you to listen more carefully where the clashes in the arrangement occur: where does the energy pile up, which parts get in each other’s way, which instrument is the first to ‘choke’ the compressor, and so on. If you get rid of these clashes with EQ and stereo placement, the need to keep pushing things up will decrease. And maybe you won’t even need a bus compressor after this, since it has already done its job as an indicator.

This problem indication also takes place on another level: if you notice that your mix responds badly to bus compression, it probably won’t work well in listening situations outside the studio. Apart from the obvious radio compression (which is a lot more relentless than your own bus compression), a listening environment with less-than-ideal acoustics can also create a compression-like effect. In a way, acoustics are like a binding agent that keeps the sound together, but if your mix lacks definition, details can easily disappear in this ‘resonant soup.’ Listening to the effect of bus compression on your mix invites you to create enough transient definition to withstand this, whether you’ll eventually keep the compressor on your mix or not.

Bus Compression to Increase Dynamics?

The reason for using compression on groups of instruments or an entire mix can be somewhat puzzling at first. It seems much less flexible than controlling the dynamics of individual components directly. Because everything is interrelated, the negative side effects of compression can make an obvious appearance across multiple instruments, which makes setting up bus compression a delicate task. But once you familiarize yourself with this procedure—and with the mechanics of mixing through a bus compressor—there are benefits to be had. Just take a look at Figure 12.2, which shows you how a bus-compressed mix can appear to be more dynamic than a mix that uses compression on its individual components, while technically the two don’t differ in dynamic range.

Figure 12.2Two ways to control the varying dynamics of a four-voice choir part, which was recorded using close microphones on each of the voices. Each voice is depicted by a different color, and the height of the rectangles symbolizes the level of each voice in the mix. The goal in this example is to even out the dynamics of the choir as a whole (the combined height of the rectangles). A compressor for each individual voice does the trick, and the resulting blend is very even for each of the chord repetitions (B). A bus compressor on the mix of the four voices retains the different internal balances in each chord, but controls the overall dynamics equally well. So if you are happy with the balances and contrast between the various elements in your mix it’s better to use bus compression, while if you need to even out these balances it’s better to use individual compressors.

If you want to properly assess the effect of the compression you use, it’s important that you don’t just compare short sections. Putting compression on a mix changes all the dynamic proportions, including those between the intro, verses and choruses. If you only listen to the effect on the chorus, you won’t know if it still has enough impact compared to the intro. This makes the musical effect of compression far more difficult to judge than that of EQ or reverb.

12.2 Choices and Settings

Just like the selection of glues on offer at the hardware store, the range of bus compressors is pretty overwhelming. But what makes a ‘regular’ compressor a good bus compressor? The simple answer is: as soon you put it on your mix bus, the transformation is complete. And if it sounds good, you don’t have to think about it anymore. But there are reasons why some compressors are more favored for the entire mix, while others are mainly used for individual tracks.

The most important feature is that you can adjust the settings of the compressor accurately enough, since the role of a bus compressor can vary per mix. If you want to create a better blend between the vocals and the accompanying instruments in an acoustic song, the best choice will be a mild compressor that mainly follows the vocals. For example, a compressor with a low ratio, soft knee, slow attack and signal-dependent release can work well. But if you want the drums to make the entire mix move more, you’ll need something with a response that’s quick and tight enough to follow the drums. A compressor with a slightly harder knee and signal-independent attack and release times can suit this purpose. For most applications, it’s important that you can set the ratio low enough, as high ratios will flatten the mix too much. And compressors that add a lot of distortion are often a bit too extreme to apply to the entire mix. In summary, for bus compression you need a compressor with versatile settings and a relatively clean sound, unless you have the luxury of choosing a specific compressor per project that works well for that particular mix.

Figure 12.3The timing setting that you choose strongly affects how the elements will be glued together in the mix. A slow attack (A) places more emphasis on the rhythm: the drum hits (black dots) will be largely allowed to pass, while the sounds that follow immediately after are attenuated. This can give the entire mix more punch and a somewhat dry feel. Conversely, a fast attack (B) already attenuates the mix during a drum hit. If you make the drums extra loud at the compressor’s input, they will push the other instruments away when they play. As a result, the drums will seem louder than they actually are, while the rest of the mix will have less punch and more emphasis on the sustain—so it will feel less dry.

12.3 Multibus Setups: Painting on a Colored Canvas

As mentioned before, bus compression isn’t used to reduce the dynamics of your mix, but to increase the cohesion between instruments. However, since reducing dynamics is the core business of a compressor, it’s impossible to create more cohesion without also flattening the dynamics of your mix. Sometimes this is a problem, especially if you’re leaning heavily on compression to mold things together. To counteract the sonic shrinkage that can occur as a result, you can spread the mix across multiple mix buses, each with its own bus compressor. This way, many hands will make light work, instead of one compressor having to deal with everything at once. The fun thing about this system is that you can choose a number of different compressors, each of which enhances a different musical aspect and produces a different kind of blend. You can see this approach as painting on a colored canvas: your canvas influences the place that’s given to a particular element in the painting. The famous mixing engineer Michael Brauer has turned this into his trademark, but many others have also used versions of this method for years.

Mix buses that are designed to give sounds a specific place can make it a bit easier for you to set up your mix. You can see it as a way to automatically apply the correct incidence of light while you paint. If you really want to highlight a particular element, you can place it in a lighter zone than when it plays a supporting role. If an instrument contributes to the rhythmic foundation, you send it to a bus that emphasizes the rhythm. A lead instrument goes into a bus that brings the sound out to the front. An instrument that’s tonally important goes into a bus that emphasizes the sustaining character of the sound. This system makes it easier to balance things quickly, because you have more zones to play with than a white canvas can offer you. On a white canvas, you would have to reinvent the wheel for every element you add in order to position it in the whole. Predesigned mix buses provide a shortcut for this, and of course you can still fine-tune the sound as much as you want after you’ve outlined the general shape of the mix.

Figure 12.4An example of a setup with differently colored mix buses, which reserve specific places in the mix for the sounds you send through.

It might sound crazy to mix with a setup that instantly affects a variety of parameters, but the interaction between your setup and the music makes it easier for you to make certain choices, because they will immediately sound more convincing. It’s as if your setup helps you to hear when your balance is on the right track. Developing such a colored canvas takes time, and the effect of it is more subtle than a lot of beginners think. Caution is advised though, as a colored canvas can also adversely affect your mix, for example by flattening the dynamics too much. In that sense, it’s no different than using a single mix bus compressor. To keep an eye on the influence of the setup, in case of doubt I sometimes switch to a fourth bus. This bus sends the sound into the mix without any manipulation, so I can always check if the tools don’t get in the way of the music.