Feature: Groups & Buses
Processing multiple sounds as a single group or bus track has long been a mainstay of professional mixing. It helps instruments gel together, can simplify complex projects and can be used for creative effects too. Let’s see how it works...
Whether you’re recording live instruments for a rock production or stacking synths and samples to create electronic music, modern productions are often complex, and are comprised of many channels. As track counts soar, projects become messy and unmanageable. Thankfully, all digital audio workstations allow you to consolidate your signals down to submixes, to aid workflow and help you keep hundreds of separate channels under control.
But mixer grouping and routing aren’t just functional considerations – they also open doors to creative signal processing and sonic exploration. Intricate routing tricks, send/return effects and parallel adventures can turn fairly basic productions into something far more experimental and creative.
So to set you on a path to mixing mastery and sound design wizardry, we’ve put together this guide to signal bussing, audio routing and processing. To see and hear our tips and tutorials in action, check out the included audio files and videos.
To begin, let’s get to grips with the basics of bussing and routing in your DAW’s virtual mixer. As most producers now work predominantly in the computer, we’ll focus on software routing here, but these techniques all stem from traditional mixing consoles, and so can be applied in the hardware realm, too.
Groups & buses
All software hosts allow you to create what’s called a group channel or bus, which is essentially an empty channel. By routing the output signal of several individual channels to this single group, you can process that collection of signals as one. You can still go back and do whatever you like to the individual tracks, but you then also have control over that final group. This, for example, allows you to funnel lots of individual drum channels to one overall ‘drums’ group, or multiple vocal layers to a master ‘vocals’ bus. You can then adjust the volume and pan of the group, as well as apply processing.
An auxiliary or return channel is also an empty channel that can be called up in your DAW’s mixer. However, instead of routing individual channel outputs directly into this, you instead use a channel’s send fader to route its signal to the aux in parallel. This is most commonly used for reverb and delay effects: load a reverb effect on a single aux return, and you can pipe portions of your channels’ signals to this aux. This will leave the original channels untouched in the mix, but their signals will hit the aux, and the reverb will be output via this channel. The concept of pre- and
post- fader routing is also important. Let’s say you’ve got a clap sound in a track, and heavy EQ is applied directly on that clap’s channel. If you route the clap to your reverb aux track post-fader, the signal that will hit the aux will be the EQed signal. Alternatively, if you route the clap signal pre-fader, the signal that hits that reverb aux will be piped before the clap channel’s insert effects and volume fader. This can be useful if, say, you want to set up a custom headphone mix for a vocalist, completely independent of the main mix balance you’ve perfected.
Before we get onto processing scenarios, let’s cover a few essential bussing strategies.
The most fundamental reason to funnel individual signals to dedicated groups is to aid workflow and make large projects more manageable. The majority of producers mix mostly in-the-box, and unlimited channels can be added at will, which means that a busy DAW project can easily get out of hand. By grouping, say, your ten-or-so individual drum channels to a single drum bus, and then your multiple vocal channels to one unified ‘vocal’ fader, and your synth parts to one main ‘synths’ group, etc, you can keep more of a handle on those collections of sounds. Then, if you have ten or so vocal layers that need a touch of brightening, it’s far easier to apply one single treble boost to the vocal group as a whole, rather than use separate EQs on each vocal channel. Not only does this and help you in a hands-on sense, but can also aid the psychological and motivational process of actually finishing a track or mix – a session packed with hundreds of channels can be mentally daunting, but tackling a few well-named, colour-coded groups is much more surmountable.
Bussing to mix
In terms of mixing, the most widely-discussed reason to group several individual signals is to sonically bind said tracks together – yep, we’re talking about that abstract term of ‘glue’. Using drums as an example, you obviously need a degree of control over each individual sound (kick, snare, hi-hats, overheads, etc), but ultimately you may need the listener to perceive those separate drum sounds as a unified ‘kit’. That can be achieved by routing those drum channels to one single ‘drum bus’, then processing them collectively. And of course, the same can be said for layered bass synths, multiple vocal takes, and so on.
Once grouped, it’s usually bus compression that’s known to bring those signals together and provide that aforementioned glue. The G-Series Compressor originally found on classic SSL mixing desks (and most well-known for its use on the master bus) is probably the most classic design of them all, known for its superior ability to unify and ‘gel’ disparate signals in a subtle yet pleasing way. Traditionally, a slow attack setting allows initial transients through, but then gently rides the sustain elements down a touch to bring them together subtly. And that word – subtle – is key here. Low ratios, slow attack and only a dB or two of gain reduction is usually all that’s needed to tie signals together to sound like a more cohesive whole without completely disrupting transient detail and the careful balance you already created.
There are, of course, occasions when you can throw the rulebook out the window and impart far more assertion and creative processing to subgroups – especially when you’re layered parts in more of a sound design sense – and we’ll be looking at approaches like this later in the feature.
Traditionally, bus compression can be applied at any point in the process, but many mix engineers actually like to set up this kind of compression at the
start of mixing, so they can balance and level elements of the mix into the compression right from the word go. There are pros and cons to this approach: the compressor’s flavour will become a part of your master mix or submixes just as much as the individual sounds, but you need to go easy and make sure you’re achieving the result you want, rather than just compressing because it’s the done thing to do.
There are occasions when you can throw the rulebook out the window