You may have heard of buss tracks as a way to process multiple tracks at once. But what exactly is a buss track? What are benefits of using buss tracks and how do you use buss tracks in your mixes?
By definition a buss track is a track that receives audio from other audio or MIDI tracks. You can think of your Master channel as a buss track because all of the tracks in your song route their audio output to the Master. This allows you to process your entire song as one track. Ableton and most other DAWs allow you to buss any tracks in your mix together and then send the signal from the bussed track to your Master. Imagine you you have three different vocal tracks in your song and you would like to automate a filter sweep on all three vocal tracks. Rather than add a filter and automate a sweep on each track you could buss them together and use a single filter on the buss to automate the filter sweep.
As you can imagine there are several benefits of using buss tracks in your mix. If we use the vocal buss track above as an example, you can see that using a buss track to automate your filter sweep will save CPU power. Instead of adding three instances of auto filter and automating three different tracks you only need one Auto Filter and one automation lane. Not only does this allow simplicity and reduce redundancy in processing but fewer devices and less automation reduces CPU load. By processing similar tracks on a single buss you can also 'glue' tracks together to make a more cohesive mix. A classic method of 'glueing' tracks together is to apply EQ and gentle compression to the buss tracks. Finally, buss tracks can assist in arrangement. Ever want to automate a volume ramp on more than one track during a buildup or mute certain tracks in your song in a breakdown? Buss tracks can help you do this quickly and efficiently in an organized way.
A great way to take advantage of benefits of buss tracks is for your drums. In any given song it's common to have several different drum tracks. Here's how you can route them to a single buss track using the I/Os in Ableton:
Once you've bussed your drums together the question remains: how can you process them? Typically you would start with EQ Eight to scoop out the lows. If the drums need more sparkle you might add a slight boost to the high shelf. It's important to consider that when you're EQing a buss track you are applying the EQ to all of the tracks routed to the buss. As a result you probably don't need dramatic EQ moves to sweeten the sound. If you find you need to make a monster EQ boosts or cuts on your buss tracks, you are probably better off going back to the specific tracks (snare, hats, kick etc..) you are having issues with and tweaking them individually.
After you've made the desired EQ tweaks, your drums can benefit from the use of a transient shaper to accentuate the transients of the drum hits and fine tune the sustain of the drums. Ableton doesn't have a dedicated transient shaper but they are easy to find. I personally like Schaak Audio Technologies Transient Shaper. It has a retro interface with four knobs that are easy to understand; the attack knob increases the volume of the transient, the release knob decreases the length of the hit, the gain knob controls the overall output volume and the drive knob adds a rich analog type saturation that works great on drums (and almost anything else for that matter).
Sometimes subtle compression (2:1) with medium attack and release times can help even out dynamics and glue your buss together. Ie. Make several tracks sound more like a single voice in your mix. The goal is not to crush the drums, but to apply a small amount of gain reduction ( maybe 3 dB).
The next round of processing I employ to my drum buss is parallel compression or NY compression. In a nutshell, parallel compression allows you to have the thickness and energy of heavily compressed drums without obliterating the transient and punch of your drums. To achieve the effect you can use any compressor with a Dry/Wet control. The workflow is simple. The first step is to slam your drums with aggressive compression, set a fast attack time and a high ratio such as 10:1. Now, drag the threshold down so you get a significant amount of gain reduction. Adjust the release so you are reducing the gain of the transient but allow the the decay of the drums to come through with minimal compression. Now you have heavily compressed drums and although they will have a higher RMS volume, they will have probably lost the punch of the transient. To bring back the punch of the drums, start mixing the the dry signal with the heavily compressed signal using the Dry/Wet knob on your compressor. If done correctly the end result should be drums that have the aggressive loud character of heavily compressed drums but maintain the punch and definition of uncompressed drums.
Using buss tracks can help you achieve a more coherent mix while speeding your workflow and saving CPU power. There are all kinds of additional buss processing you can perform to dial in your mix and add creative flare to your song. Try parallel distortion (Saturator, Dynamic Tube etc...) on your buss tracks, play with Mid/Side processing, or apply stereo effects (Reverb, Simple Delay, Chorus etc..).
If you want to learn more about buss tracks and how to improve your mixing check out Beat Drop's Mixing and Mastering class taught but Timothy Allan.