What is a Mix Bus, a Master Bus and Bus Routing?

by ReverbLxnd in Mixing

What is a Mix Bus? What do you put in it? What is Bus Routing and what is the Master Bus? This is an easy topic, let's answer these question w/out needlessly complicating things.

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Today we are going to look at what a mix bus is and cover a few ideas for how to treat the mix bus.

This is such an easy simple topic and we’re not going to needlessly complicate things (in traditional of finding the easiest way of breaking things down).

I often tend to jump into a few DAWs here and there but don’t worry if that’s not what you’re using. Even though the navigation or interface and some menu options might be different, basically all DAWs have the same bells and whistles under the hood.

The concepts and capabilities are largely the same from DAW to DAW.

Let’s kick things off by looking at what a bus, and a send, is.

Logic Pro has a send option with a blank knob next to it, perhaps that unique but the idea is the same for most DAWs.

You start with the option of having a send in place and then you can pick and add a bus. As soon as you pick a bus, it creates an auxiliary channel.

Right there in that one moment in time, you just ran through send, bus, and auxiliary all at once — bus routing in other words.

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What is Bus Routing?

Bus routing is essentially having different buses for different sections of the mix.

Let me explain…

If you’ve got drums (kick, snare, hi-hat, toms, overheads, room) and then you have all of the other instruments, such as bass, guitars, vocals, and so on, then you will have soo many channels all going into the master bus.

It’s a little bit hard to keep control of all these different instruments.

But if you create an auxiliary channel and you put all the drums there…

…and then create a different one and put the bass there, and create a different one and put all guitars there, and so on…

…you will have a much better way of controlling tracks, doing automation and applying compression to your mix.

Where Do You Apply Bus Routing? What to Put on a Mix Bus

The simple answer—apply the bus for everything.

Create a bus for the drums, for the bass, for the keyboards, for the synths, for the guitars, vocals, and so on.

In other words, you shouldn’t leave anything out.

In fact, you for something like the drums, you can have a bus just for the kick drums.

Say you’re going to use a kick drum, and then a second kick drum, and then a parallel kick drum. In this case, you can create a sub-bus just for the kick drum, which then goes into the drum bus, along with all the other instruments.

The more you use buses, the more control you’ll have over your final sound.

What is a Mix Bus?

The concept of a bus is music really quite simple — it’s simply anything you can put more than one channel into on your DAW.

A bus is simply a way to move an audio signal from point A to point B.

Your mix bus, also known as the 2 bus, is your main fader. It is the main output fader on any DAW.

For the uninitiated, the master bus is the main left-right stereo output bus in your DAW. Different DAWs might have different looking mix buses but as I said, they all function in the same way.

It is also where a lot of producers decide to add a few tools and toys to shape the sound on a global bird’s eye level.

Some producers might choose to leave their master bus empty, some choose to do a little bit of processing on it, others throw the kitchen sink at it.

This article assumes you’ll be doing at least some processing on the master bus and provide some helpful suggestions on how to get started.

What is an Aux-Send?

You send an audio signal from a track to a bus, and then the bus is routed into an auxiliary track.

The input, for instance, can be “sent” to a certain bus, say, bus 1.

Aux is short for auxillary.

Why is auxillary?

Because every track will have it’s own input and output (to, say, a stereo channel), this send to a bus is a secondary output (bus 1 in our example).

That send will go directly into the auxiliary track.

You do need to actually send a certain amount of the signal to that bus for it to actually make it’s way to the auxiliary track.

There’s usually a dial for selecting how much of the audio signal is to be sent.

Are buses used just to send audio signals to an auxiliary track?


They can also be be used as routing options to move your audio signal from, say, one track to a sidechain input of a plugin on a different track on the same project, for instance.

If a bus is a way to move an audio signal from point A to B, the send is just the point at which you’re allowing audio to be routed somewhere else.

The main thing to understand about routing signals and using buses is how your send is set up.

You have three main options in modern DAWs.

  1. Pre fader
  2. Post fader
  3. Post pan

Logic Pro does a good job of differentiating the three modes for you visually using a menu option so at a glance you know how each send is set up to the individual buses that you’re routing to.

Pre Fader

Pre fader mode means that you are sending an audio signal from a track to a bus before the fader. Which means your fader could be set at whatever decibels (even completely off) and the send signal won’t be affected.

Whether your fader dial is set to 20 dB or 0 or completely off, it doesn’t really matter.

Only the send dial is controlling the audio signal sent through to the secondary bus or buses.

Pre fader means direct to the bus.

Post Fader

Post fader mode simply means that your audio signal is flowing through the fader first and then it goes to the send.

If your fader dial is set a -4 dB, that means you are sending -4 bB of your audio signal out through your send dial to your bus.

The send dial becomes relative to what is sent through from the fader dial.

Post Pan

Post pan means that the audio signal is going to go through the pan dial for the track before it gets sent to the send and the bus thereafter.

This is really important because you could have many tracks in one project, all going out being sent to the same bus.

If you spent all this time, perfectly positioning yo*ur sound in the stereo field, with your pan knob on each track, and then you send it all in any mode other than post-pan, everything will be right back in the middle of that stereo field again.

All of a sudden, that reverb, that compression, or whatever it is that you got set up on that auxiliary track, will have a space war of sorts.

There is no room for anything because everything is in the same exact spot in the stereo field.

Post pan will take the pan position of each track into consideration as it’s being routed through that bus to that auxiliary channel.

If you have something panned hard-left, it’s going to be panned hard-left on that auxiliary channel.

What is Bus Compression?

If you’ve been reading this blog for a while, then you probably already know that it is best to use very little compression many times (unless it’s parallel compression).

Using buses allows you to put compression easily in different places.

For instance, if you have a bass that is recorded both direct and through the cabinet, then you will have two channels —

  1. Parallel compression for the bass.
  2. The other channel(s) go into your bass bus.

You can have a chance to compress at least twice, and a third time on the bus.

That means you can be able to compress very little many times.

You can even add a little bit of a limiter on the bus.

You just have to maintain that level down and make the limiter work just a little bit.

What is Bus Automation?

Instead of using ten fingers to automate the drums (one per channel), you can just have a bus, and control the overall level of drums with one finger.

That is saving a lot of time.

In fact, having a different bus for each group of instruments will allow you to control the automation of multiple sections at the same time which will make mixing a lot more effective.

What is the Master Bus?

Finally, the master bus.

The terms master bus and mix bus are sometimes used interchangeably but they don’t always mean the same, especially in complex mixes.

All of this mix architecture that we’ve been talking about is designed to achieve a better sound on the master bus.

Each bus that we’ve been preparing will be summed into the master bus.

The master bus is the bus that sums all the other buses that make up a mix.

The fact that you have divided all of your sections into individual knobs will mean that your master bus will be a lot easier to control.

The master bus is where your final mix comes out. Working with a well-structured mix will help you achieve a much better sound in a much more effective way.

It is the master channel into which all the different mixes lead.

In Conclusion

When you send audio to a bus, the bus routes it somewhere (whether it’s going to be used as an input in an auxiliary track, or used as a bus on a trip to a sidechain input on a plugin).

We talk about mixing techniques and a lot more in our mixing blog. Have a look if you’re interested in learning the art of mixing.

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That’s it for this article.


I've been a musician and brought in my stuff for mixing and mastering, I've been my own producer where I wrote, recorded, mixed and sold my own stuff. Now, I'm *mostly* an audio engineer, where I only record and mix for clients. I'm currently based in Berlin, Germany, where I operate ReverbLand out of. Got a question? DM me on Instagram or Twitter @reverblxnd everywhere, or shoot me an email [email protected]. I'd love to hear from you.

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