Mixing is a lot like baking. Just throwing stuff into a bowl and hoping for the best will never give you the best results. In this blog, we seek to explain what a mix bus actually is and how you can best prepare your instrument groups before sending them all through the master bus of your mixer or DAW. In other words: we explain how to bring structure to audio mixing.

Mixing with the Mix Bus

What is a Mix Bus?

You could compare a mix bus with the bowl you mix your eggs, flour and sugar in before baking a cake. If you’re baking something simple, you’ll only need one bowl which, in the audio mixing world, is your master bus – the thing you send all of your stems and mix busses through. When working with a more complex recipe (think a multi-tier birthday cake in the shape of your favourite superhero) then you’ll quickly need a few more mixing bowls. The same is true of audio mixing. All of those different groups of ingredients will need melding and prepping using your mix buses before you finally blend everything together to build your masterpiece (via the master bus). If you’re working with a DAW, then in theory, you have an unlimited number of mix buses at your disposal, so you can create channel groups per mix bus, feed them through one another and apply all the effects you want. If you’re working with a physical mixer, the options are a little more limited, since there’s literally less space. And with smaller mixers, you often don’t even have the option of making channel groups.

Dynamic Control via the Mix Bus or VCA Fader

Say you send all the guitars or all the different elements of a full drum kit to a single mix bus. From there, you can control the volume level of that whole group with just one fader. You can also inject some extra dynamics into specific passages by using automation to push the volume of your grouped instruments up or down at just the right time. Basically, by using the mix bus, you won’t have to make these tweaks for every single stem.

A handy alternative to using a mix bus is a VCA fader. By making a VCA group, you can then send the level faders of every stem within the group to your VCA fader. One of the biggest bonuses of using a VCA fader is that any effects controlled via a post-fader send, like reverb or delay, remain in proportion to their audio source. However, a VCA fader isn’t actually part of the audio chain, so you can’t apply any audio effects to it.

Putting Compression on a Mix Bus

Compressors behave very differently when applied to a group of instruments rather than to individual instruments. When treating an individual instrument, the compressor is only triggered by that instrument, and the effect is only applied to that single instrument. When treating a group of instruments, the compressor is triggered by the loudest instrument in the group at any given moment, so the compressor has an effect on all of the instruments within the group. In a drum bus, the compressor is likely to be triggered by the kick and snare, meaning that the compressor will then apply gain-reduction to every channel that’s being sent through the drum bus – including the cymbals, which are mainly heard via the overheads. This is referred to as ‘bus compression’, and can give you more cohesive results by ‘glueing’ everything together.

Tip: Multi-Band Compression & Side-Chaining

A tried-and-tested technique for creating more space for the vocals is to take all of the other melodic instruments that sit within a similar frequency range to the vocals and stick them through one mix bus. This basically means all of the instruments other than the drums, the bass and the vocals. Now, you’ll want to insert a multi-band compressor on that bus and set it to focus on the 1 to 5kHz frequency range, which is the region where vocals gain most clarity. Here, it’s important to use a multi-band compressor with a side-chaining option. This makes sure that the compressor is ‘listening’ to a selected audio source, which can be an entirely different audio source to the channel you’re applying the compression to. In this case, we make sure the compressor is listening to the vocals. As a result, all of the other melodic instruments are slightly dulled, but only when the vocals are present.

Bon appetit!

What do you use your mix buses for? Let us know in the comments!

See also…

» Mixers
» DAWs

» Mixing with Inserts & AUX Sends
» What do you need to produce music?

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