An informative article about mixing and audio engineering term Bus Tracks

Many DAWs like Pro Tools, Logic Reason or Garageband feature mix busses, aux tracks, group tracks. All of which essentially serve the same purpose, but what is a mix bus track anyway?

What is a Bus track in Mixing?

A bus track is like a master track or a summing track for several other tracks. Bus tracks can be used for things such as sending all your drums to a drum bus, or using  reverb , compression or effects. The master bus or Stereo bus, refers to the left and right output of all the other busses. The Master or Stereo Output Bus  sums together all the tracks for your final stereo mix. A bus track my also be called an Auxiliary or AUX track. A bus track or bus is the sum of several different signals, usually with its own fader to control the overall vouleme. If we send all the drum microphones to the drum bus track, then the drum bus fader controls the output of all those tracks. In the analog world, a bus is a physical connection of copper, or in the digital wpriu;d, a sum digitally of all tracks sent to the bus.

Pre Fader or Post Fader (Sends)

Usually Busses are post fader or after the fader. In other words, whatever level you send with the fader is the amount of singla you send to the bus. Busses offer track manipulation as a group, which is often useful for things like equalization and compression. It is common, in a mixing project with many vocal tracks, to send all the vocals to a vocal bus, where EQ, and compression affects all the tracks. When you set up a reverb or aux bus, you may send it pre-fader, or before the fader with an aux send. When you use an aux send for reverb pre-fader, you specify how much signal to send to the reverb bus, but the fader does not affect the level sent. For example. if you want to send the drums to reverb, but not any other tracks you would send level from each of the drum’s aux send to a reverb bus, but not send any of the tracks you don’t want reverb.

An example of post fader bus, would be assign all the drums to one bus, and then when you need to bring up all the drums, instead of bringing up each of the tracks individually,. you can bring up the drum bus fader and raise all the volumes of your drum tracks. When you solo the drum bus, you should hear only the drums, or if you mute the bus, drums should disappear.

Sidechaining and Advanced Mixing Techniques

The more tracks and effects you start adding, the more essential bus tracks become. It’s easy to get many tracks in a project after awhile, and making a submix of each element can help you manage more complex musical processes. Sidechaining, is where you use a send or key from one bus to affect another. An example would be sidechaining output of the drum bus the  to the compressor on the synthesizer bus. This means the compressor input sidechain is linked to the drum bus signal on the synthesizer track. So when the drums hit, the synth track compressor will be triggered, pulling the synth track down when ever the drums hit. This pumping effect is common in  EDM music.

In addition to all that, bus tracks allow you to use your analog effects on more than one track, or in the digital realm, save processing power, by using only one instance of an effect, instead of having to put a separate instance of a plugin on every track. Reverb and delays, as well as many analog modeling plugins such as tape machine emulation are very CPU heavy, and tend to stall the computer out if too many copies are added to a project. Its easier to add one instance to the bus track, or set up an auxiliary track for an effect, than to have to add an effect.

Busses for Headphone Mixes

Buses are also often used for headphone mixes. Since a bus send can be sent to a headphone amplifier, it makes a pre-fader send from whatever channels you want sent to the headphones easy! The AUX tracks on an analog mixer are most commonly used this way for headphone mixes.  Since mixers usually have several aux tracks, a separate mix for each musician can be set up with a separate level for each player. Usually, Busses are setup as pre fader for headphones and monitors, and post fader for reverbs, delays, and other time based processors. This is so that you can bring down the fader, and no signal will be sent to the reverb. If the bus is set up pre fader for a headphone mix, and you bring the fader the whole way down, the signal is still sent to the auxiliary track. Likewise, if you bring the fader down on a pre fader bus send for a headphone mix, it does not bring down the level sent to the headphones connected to that bus.

Busses and Automation for Creative Effects

Bus use can lead to more creativity in your mixes. Once you realize you can send signal to a bus just to try something out, you end up adding a little bit of this and a little bit of that, and mixing it all together for something really cool. Instead of adding 100%, you can set up a wet or (affected sound) or a dry (unaffected)  which can really make your mixes more interesting. You can apply automation to a bus, or automate the send to a bus to differentiate different parts of a piece, which can really help your mix explore different interesting effects and special parts that sound interesting and bring your mix to life.