Logic Pro X - Busses vs. VCAs vs. Groups vs Track Stacks | What's the Difference?
Logic Pro X offers a whole plethora of channel grouping options for mixing. There’s Busses, (aka Bus Channels or Submixes), VCAs, Track Groups, and Track Stacks. VCA channels and Track Stacks are inherently new to Logic v10; however, routing multiple tracks to Auxiliary Channels via Busses and using Track Groups has been around for a while. Let’s break down the differences between these.
Busses / Bus Channels — In Logic Pro X, you can create an Auxiliary Channel Strip, or Aux Track, as I usually call it, and then route the output of multiple channels to the Aux Track in the mixer. The term that’s typically used here is creating Busses, Bus Channels, or Sub Mixes.
By routing multiple channels to one Aux Track, you are summing the output of multiple channels into one. This allows you to have a master volume control over the entire summed signal, and this also allows you to add effects inserts and process the entire summed signal as a group.
I typically use this for bus processing. For example, I like to group all of my drum tracks this way, and then add some stereo bus compression, like the Waves API-2500, to ‘glue’ the group of drum tracks together. I’m also a big fan of using tape saturation on the drum bus. I do the same with guitars, but I often add an exciter or saturation to those.
You can also route channels off of the Sends in order to use the Aux Track as a source for time-based effects, reverb, delay and chorus; or for parallel compression. However this is usually called creating an effects send, not a submix; so it’s similar, but a bit different use.
VCA Channels — VCA stands for Voltage Controlled Amplifier. VCAs are often very confusing for people new to audio, especially those that have never mixed on an analog console before. VCAs are a voltage control source to control level of multiple channels simultaneously. When you create a VCA group out of multiple channels, this allows you to control the group of channels’ volume with a single VCA fader. Sound a lot like a bus, right? Well, VCA fader differ because they do not pass signal. VCAs are just a control source, not a summing channel, and since they don’t pass signal or sum the output of channels, you cannot add inserts or sends to them.
VCAs sound like a disadvantage, right? — Nope. There are a lot of situations where you may NOT want to sum the output of channels. There is no need to in some situations. Summing channels for the sake of summing (at least in the digital realm), has no advantages and actually offers some disadvantages when dealing with noise floor issues and maintaining relative volume balance among all channels in the group. If you’re main purpose is to control multiple channels as a group — use a VCA. If you need to sum channels for bus processing — use a Bus.
Track Groups — Creating Groups for multiple channels offers both mixing and editing options. You can trim, cut, copy, paste, using flex time, comp with take folders — all as a group. So those are some extra editing capabilities that busses, VCAs and track stacks don’t have. But what about volume control? From a signal flow standpoint, there is no difference between creating a VCA group and creating a Track Group to control the volume of multiple channels at once.
I typically reserve Groups for editing functions, and use VCAs for mixing, and here’s why — Let’s say that you want to adjust the fader of one or a few channels in a group. You would have to press Shift-G to deactivate the group, make your fader changes, and then press Shift-G again to reactivate the group. With VCAs, you don’t need to deactivate/activate anything. Just make the change to the individual faders, and go on about your business.
Track Stacks — There’s two types of track stacks in Logic Pro X: Folder Stacks and Summing Stacks. The good news? These are just VCAs and Busses in disguise! From a signal flow standpoint, Folder Stacks are identical to VCAs, and Summing Stacks are identical to submix Busses. Track Stacks have the additional benefit of organizing the VCA or Bus at the top of channels for a cleaner look.
Conclusion — If you you want to sum and buss process, use Summing Stacks. I end up using this option 90% of the time. If you don’t want to sum or apply buss processing, use Folder Stacks. I reserve Groups for editing functions.