Pro Tools Fundamentals - Understanding Busses

10-18-2014 10:00 AM

Back to basics this week with a look at busses. These are a very common source of confusion for novice users. Exactly what busses are and how you might use them is so important that even if you think you’re getting by without them, you’re already using them in your sessions even if you don’t know it yet.
What Is A Buss?

A buss is an internal connection within Pro Tools and it can be used to send combinations (or “mixes”) of signals from place to place within the mixer. If you have never come across the word before its worth noting that this isn’t Pro Tools terminology and busses are used for all sorts of data, not just audio. Any channel can be routed to any buss. Even if you think you have never used a buss in a session you will have, as the main output of your session is a buss in pretty much the same way as the internal busses to be found under the buss menu in the output selector: Any combination of channels can be routed to a single destination - sounds like a buss to me! If you find the idea of busses difficult then the best way to understand them is to use them. Here are five ways you can use busses in your sessions:

1. Submixes

By assigning tracks which “belong together in some way” (I’m deliberately avoiding using the word group here…) to a buss instead of the main output it is possible to bring these tracks together for processing on a shared aux input. This can be done for convenience, as more sources can be processed through fewer plug-ins or because it sounds different. The most obvious example of this is the difference between compressing source tracks individually or submixing the source tracks and compressing the submix through a single compressor. While in both scenarios all the source tracks get compressed, the results from these two approaches sound significantly different. Many new users assume that the reason for creating submixes is for level control but mix groups exist for this purpose. While you can use subgroups for level control the real point of them is to bring audio together for processing. The other really significant use for submixing via busses is for creating stems. It has always been possible to route via a buss to an audio track instead of an aux input. In the bounce to disk dialogue alternative sources other than the main output can be selected and the output of a buss can be bounced in exactly the same way as the main output. The facility to simultaneously bounce multiple stems in Pro Tools 11HD makes this process particularly painless but real time printing of multiple busses to multiple tracks is available to everyone.

2. Effects Sends

Another very common use of busses is in setting up send-return loops for sharing time-based effects across sessions. By using auxiliary sends to send the desired signals to the input of a plug-in inserted on an auxiliary input, that effect can be shared across as many tracks as you like in your session. Take a look at this video from earlier in the series if you haven’t ever tried working this way.

3. Keying

A third use for busses is for routing signals as external key inputs to side chains in dynamics processors. By using a signal to control an aspect of another signal things can get very interesting. While Pro Tools uses a traditional approach to side chains and key inputs which mirrors the way these things were done on analogue equipment we are seeing more and more software which allows audio tracks to modulate almost parameter rather than just dynamic processors. Take a look at this (members only) video I did some time ago on using external side chains for a thorough exploration.

4. Multiple Busses Using Ctrl

The fact that a track can be routed to more than one buss at a time becomes apparent fairly quickly when you start to use auxiliary sends. If you want a signal to go to multiple busses at the same time then sending to one buss from the main track output selector and a different buss from a send is fairly straightforward. If you want the level going to both busses to follow the main fader then create a post fader send (the default) and if you want them to be independent of each other create a pre fade send using the blue “Pre” button on the send. Something many people don’t realise is that it is possible to assign the main track output to multiple busses by holding Control (Start on windows) and assigning to another buss or output. A “+” will appear in front of the output to indicate that multiple outputs have been assigned. Use this anywhere you would use a post fade send left at unity to duplicate an output.

5. Mapped Output Busses

Since Pro Tools 9 outputs have changed from connections to physical outputs to “mapped output busses”. Essentially this means that rather than assigning directly to an output, Pro Tools assigns to a buss which is then assigned to a physical output. This system is often misunderstood but goes a long way towards alleviating the problems encountered when moving projects from system to system as Pro Tools attempts to re-map output busses to the most appropriate output on the new system. This is quite a big subject and only really affects people moving projects between systems but its important to be aware that all the available destinations that tracks can be routed to are busses, whether internal or mapped to outputs.