Using an audio bus for effective routing and mixing
When most of us think of a bus, we usually refer to our local public transportation system, and in reality these busses perform much the same function as an audio bus would in our D.A.W. or mixing console. Think about how a bus works, it has a specific path it follows and at any time someone can get on that bus and ride it to its final destination. Furthermore, there are many different busses each following their own path with their own passengers. This is exactly the same purpose of an audio bus, except instead of people, the passengers are audio signals. Also, if you think about it, a bus is only effective to get people from one point in the city to another. It generally doesn’t take you outside the city. For our purposes, the “city” is our mixing console. This is where the concept of an audio bus came to be. As recording started to get more complex and users were offered more audio tracks to work with, there was a need to be able to easily have control of those tracks. For our purposes, we will be looking at using a bus and return to control a “sub-group” of tracks. In our next article we will look at how to use busses for effect sends.
Let’s first take a look at how engineers use buses to more effectively have control of a group of tracks. In the picture below, all of the tracks that you see are the background vocals for a song. There are 24 different tracks that make up this element of our song. This is not uncommon in music production, each one of these tracks ads layer and texture to the overall element.
The problem we are faced with in this situation is one of control. We are going to need an effective way to control the overall dynamic of these tracks within the mix. At some point in time you will want to bring up the overall volume (or down) of the background vocals; and you might want to apply some sort of EQ or dynamic processing to them, or even apply some effect such as reverb or delay. Since these tracks all make up one element of our song (background vocals), we can treat them as one element and apply changes to them as a whole. This will be much easier that having to try and bring up and down bunches of faders at once.
The first step is for us to assign the output of each of these tracks to one of our busses. Then we will have to create a return track into our console for us to monitor and control the bus path. With Pro Tools 9, there are some wonderful new features that make this task super easy. First, select each of the track names you want to assign to the bus. You can do this easily by selecting the first track then holding down the Shift key on your keyboard then selecting the last track you want. It’ll look something like this:
This will allow us to assign the same bus output to all the selected tracks at once, instead of having to make the assignment on each individual track; we will save time and maximize our workflow. Now hold down the Shift key + Option (Shift + Alt on a PC) together and click on the track output selector:
You will see the menu pop us with a few options but we will be using the “new track…” feature. This will allow us to assign the output of our track to a new Aux track that Pro Tools will create for us.
This window will now pop up asking you what you would like to name your new track, what type of track you would like to create, and what width: mono or stereo. Let’s create the track as a Stereo track and the Type as an Aux Input, and we will name this one BGV: you name yours whatever you want.
What this will do for us is a few things, it will create a new Stereo Aux track in our session, it will name the Aux track whatever name you give it, it will assign the output of your selected audio track to a free stereo bus within your mixer, it will name that bus the same name as the Aux track, and finally assign the input to the Aux track as the bus output assignment from the audio tracks. Holy crap that’s a lot of things at once! It will look something like this:
Notice how all of my audio tracks on the left have the output BGV and the input into the Aux track is BGV? That’s signal flow at work. Outputs feed inputs, which feed outputs, over and over again. Everything we do with audio is based around this basic concept of signal flow.
Now we have the output of all our background vocal tracks going down a bus path, through an Aux track, then to our man output 1-2 so we can hear it out of our speakers or headphones. Ta-da! If we want to increase or decrease the overall level of our bgv element within the mix, all we have to do is use the volume fader on the Aux track since it is controlling all of the assigned tracks.
Engineers have used this technique for many, many years. It simplifies the amount of work that is needed to manage a large session. If the producer asks for more background vocals, the engineer only needs to bring up one fader instead of trying to bring up a whole bunch of faders evenly. Furthermore, you can apply a plug-in to the Aux track and it will affect the audio signal of all the tracks flowing through it. This is especially useful in maximizing the power of your system. It will take a lot more system resources to apply an EQ to every single track as opposed to one track. Since each of the individual audio tracks makes up one “element” of the song, it is beneficial to treat it and process it as a single element. Using an EQ or dynamic processor such as compressor, you can balance out the overall tone of the element in relation to all the other elements of the song. This will allow you to have much easier control of all the elements of a mix and be able to tame the workload of using a lot of faders and track controls.
For my example I am using, I have chosen to use a compressor and EQ to balance out the background vocals:
This technique is just one of the many uses for an audio bus. It really is just a pathway that connects 2 points of a console (city). The great thing is that Pro Tools and all modern D.A.W’s have a multitude of busses available: Pro Tools has a total of 256 busses (128 stereo pairs). This usage can be repeated over and over again for all of the elements of your song, drums, guitar, keyboard, etc…