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Routing and grouping techniques

October 24, 2013 - 12:00 am

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12 min read

(For more resources related to this topic, see here.)

Easy audio grouping

Pro Tools offers an interesting shortcut to assist the process. To create a new audio group, the simplest way is to follow these steps:

Select the tracks to be grouped.
Press option + shift (Mac) or Alt + Shift (Windows) and click on the track output.
Select New Track and create a mono or stereo auxiliary track. The bus name and routing will be automatically assigned.

We can later select or show the corresponding tracks associated with any type of input or output by right-clicking on any track input or output. This also works for hardware sends.

Multiple track outputs

In Pro Tools, a track can have as many outputs as you like (as long as you have available voices); it can even be routed to all available outputs simultaneously. Hold the control key (Mac) or Start key (Windows) and click on the track’s output to add another output. When a track is routed to multiple outputs, a + button is displayed like this:

Pro Tools HD 11

Routing to multiple outputs; this track is assigned to Mixbus and other outputs

There are also key modifiers that we can use.

Key modifier	Mac	Windows
Add the desired output to all the tracks	control + option	Start + Alt
Add the desired output to the selected tracks	control + option + shift	Start + Alt + Shift

Stemming with multiple outputs

Unfortunately, there is no easy way of creating stems or multitrack bounces automatically with Pro Tools 10; the process remains mainly manual. Pro Tools 11 addresses some of these issues in the next section, but for now, assuming that our master fader track contains processing, our first and only stemming option is to solo the appropriate tracks and use the bounce to disk function.

If we have no processing for our master output fader, we can bounce inside the session instead by assigning multiple outputs to tracks or buses by grouping them and creating auxiliary sends. Using the key modifiers defined previously, you can quickly select tracks and assign their outputs or auxiliary sends to new audio tracks for recording. To stem tracks to a new audio track without affecting their current routing, use the following methods.

Using multiple outputs

Select the tracks.
Hold control + option + shift (Mac) or Start + Alt + Shift (Windows).
Click on New track from the track output menu.
Create the appropriate audio track and record.

Using auxiliary sends

Select the tracks.
Hold option + shift (Mac) or Alt + Shift (Windows).
Click on N ew track from the track output menu.
Create the appropriate audio track and record.

We can select the desired recording format from the session window accessible from Setup | Session . If you’re recording the track at anything other than a 32-bit float, make sure your levels do not exceed 0 dBfs.

We can also use complex mixing routing techniques to our advantage, as this will give us many summing points from which we can easily create the New track stems. We will discuss more on how to increase routing complexity to create more summing points inside the mix.

Sound layering

Using auxiliary tracks is the best way to perform parallel processing in Pro Tools, but multiple output routing can also be very useful for sound layering, keeping your track sends free for other effects. By sending the output to multiple auxiliary tracks, we can very easily add textures and effects. As an example, I like to layer my basses this way with different distortions and other parallel processing. To me, sound layering is more suited to multiple outputs because their relative level mostly stays the same.

Stemming with Pro Tools 11

Pro Tools 11 brings new offline bouncing capabilities with added simultaneous bounce from internal busses or physical outputs. Inside the Bounce to disk window, click on the + button to add another source to a maximum of 16. Each source can have a different file format, from mono to multichannel audio.

Because we can bounce physical outputs, Pro Tools 11 also allows for stemming tracks that are processed using master fader inserts. These new features added to offline bounces have drastically improved the Pro Tools 10 workflow, saving us a lot of time and leaving us with the following two main stemming options:

While working with multiple outputs, we can source our stem from the physical outputs directly
While summing inside Pro Tools, it becomes a lot more relevant to group as many tracks as we can to create available bounce sources

Increasing mixing complexity

One of the biggest advantages of mixing inside a DAW over traditional analogue console setups is its expanded routing capabilities, giving us far more control over the signal. In this section, I’d like to discuss how to use buses to create more complex mixes, that is, creating extra summing points for several uses and comparing the digital approach over a traditional frontend analog mixing console setup.

As we saw previously, Pro Tools 10 introduced a new 64-bit floating point mixer, allowing for almost unlimited headroom and greater precision, which made digital summing even more digitally perfect. This means that it is entirely up to the engineer to create his sound textures through recording or digital processing. Pro Tools 11 took this quest for digital perfection even further with a full 64-bit path.

On the other hand, analog is technically flawed and has always been; every single piece of circuitry will color the signal in various amounts, but these are those imperfections that many of us came to love and successfully or not tried to recreate in the digital domain. A digital mixer will sum signals with a far lower harmonic distortion. Applying different distortions is therefore the key to restore an analog feel to the mix. The first step toward this approach is to increase the mixer’s complexity to be able to apply different types of distortions in many more places.

Audio groups or buses are the most basic routing idea. As an example, working with drums, I would group all the kicks together, the snare together, the toms together, the overheads together, the rooms together, and so on. Those subbuses will then be bused to a master drum bus. This allows us to do the following:

Process multiple microphones at a time
Bounce stems more easily later
Have greater control over my individual drum sounds

To me, routing is the heart of digital mixing and making it as complex as possible begins to open many new creative doors.

But we can go a step further. My drum bus will be first bused to my rhythm bus, then to my instrumental bus, and finally to my mix bus. This introduces more advanced groupings based on other criteria such as rhythm or instrumental. This might not seem very useful at first, but it will make you think about the track in different ways, giving you control at every stages of the mix. Here is an example of what a complex mix would look like:

Pro Tools HD 11

An example of a more complex routing diagram

I might not use all the possibilities all the time, and this is only a small example. But this helped me very much over the years to create better depth in my mixes and also considerably speed up my workflow while creating stem mixes. I have instant access to many more summing points in my mixes, allowing me to group and differentiate even more sounds from each other.

The previous diagram only shows how to increase a mix complexity by busing tracks into each other, but these summing points are also open doors to some very effective parallel processing.

Default output bus options

While working with multiple buses, it becomes quite hard to systematically remember to update the track output to the user’s Mixbus. We can change the default track’s Pro Tools’s default bus output through Preferences | I/O | Output | Default Output Bus .

Along with changing the default bus output, there are a few key modifiers worth remembering to assign tracks to the desired output or the bus.

Key modifier	Mac	Windows
Assign all the tracks to the same I/O	option	Alt
Assign all the selected tracks to the same I/O	option + shift	Alt + Shift
Assign all the tracks’ I/O incrementally	command + option	Ctrl + Alt
Assign all the selected tracks’ I/O incrementally	command + option + shift	Ctrl + Alt + Shift

Greater control over parallel processing

Parallel processing is widely used for mixing. It allows adding to the signal while preserving the original content. It usually sounds a lot better to mix this way rather than process everything on groups; drums can particularly benefit from this technique.

The main issue with group processing is that it tends to make everything sound very clinical and lifeless, especially if too much dynamic treatment is applied. Digital dynamic processors especially do not compare well to their analog counterpart when it comes to attenuating levels without taking life out of the recording. For these reasons, I tend to complement my mixes with a lot of parallel processing to increase harmonics, depth, loudness, and focus frequencies rather than cutting or boosting them too much. Parallel processing allows me to get a richer sound.

Creating parallel processing requires extra buses. We can use the track sends, multiple outputs, or duplicate the track to achieve quick results.

As an example, using track sends in pre fader mode, I can quickly create a perfect copy of my signal independent of my main mix level to process and automate creatively.

Select the tracks and press command + G (Mac) or Ctrl + G (Windows) to create a new group.
Inside the Create group window, disable Follow Global and select Mix or Edit/Mix and the appropriate send and settings you would like to link.In my example, I will only link Volume and Mute .

Now that we have created the group, a neat thing to do would be to copy the existing track volume levels to the send. To do so, perform the following steps:

Press command + option + H (Mac) or Ctrl + Alt + H (Windows).
The Copy to Send window appears. Select the correct destination send and the parameter to copy. We can copy everything, even automation, to have the exact same mix across the entire song.
Now with the tracks still selected, display any send window, hold option + shift (Mac) or Alt + Shift (Windows), and click on PRE to make the sends pre fader and have the auxiliary mix independent of the main mix.

Having copied the current mix to the send, we can not only use it as a perfect parallel copy, but now we also have the choice to alter the balance between the current mix and the send to better suit the type of parallel processing we will be applying. Trying to improve the low end might not require too much high frequency information, so I might change the balance to pull down the appropriate tracks. On the other hand, trying to improve my high end might benefit from pulling down low frequency content.

Copying mix to send is also very useful while setting up cue mixes for recording.

Using the copy to send function is very rewarding while working with parallel processing, but the default mixer’s send view does not look very user friendly. Pro Tools offers an alternate way of displaying the send information inside the mixer window. We can focus on a particular send to display mini fader sends and level information. To do so, let’s navigate to View | Sends A-E or View | Sends F-J and select the particular send you would like to display. We can also press command + click (Mac) or Ctrl + click (Windows) from the left-hand side of the send in the mixer view. We can display a maximum of two sends at a time in Pro Tools 10 and all of them simultaneously in Pro Tools 11, giving a great matrix view for parallel processing or headphone mixes. This new functionality is accessible from View | Expanded Sends .

Pro Tools HD 11

Pro Tools 11 Expanded Sends view, showing Sends A-E

We now have a nice send display with linked parameters:

To change the level of all the grouped tracks, keeping their relative level with the group active, just move one of the send fader
To change one send value without affecting the entire group, hold control (Mac) or Start (Windows) and move the appropriate fader

Advanced side chain

Side chaining is one of the most commonly used techniques for music production, sound design, and mixing. Pro Tools allow for some interesting side chaining possibilities, allowing us to not only mix many different tracks and process them, but also to play with their timing by manipulating the automatic delay compensation.

For bass

I will stay with my drum recording and take the classic example of compressing the bass track according to the kick. By doing so, we make the groove tighter, reinforcing the impression that the bass player is locked to the drum groove. To do so, I could use the Bomb Factory BF76 plugin on the bass with my side chain activated on bus 15 carrying the kick.

Once it is set up, every time the kick hits, the bass track gain will be pulled down, enhancing the groove and also giving more space in the mix for the “kick drum,” but that is not all. Since Pro Tools uses buses to create external side chains, we can send as many signals as we’d like to control the bass accordingly.

As an example, I could have the kick not only during the verses but could also add some of my percussion to the side chain mix. Tweaking the side chain balance mix can give you very natural results and give the impression that the bass player is grooving more with the entire performance.

When we group multiple signals together into a side chain, we can also alter their frequency spectrum or even their dynamics to create different compression behaviors. Because my side chain information is contained on a bus, I can create a master fader or auxiliary track to process the audio before it reaches my plugin. While working with recorded drums, it might be useful to gate the side chain bus a lot more aggressively, since it cannot be heard. We can also boost one of the low kick frequencies and cut the high end to avoid hats, crashes, and so on triggering unwanted compressions. To do so, we could boost the low frequencies first and then gate the result more aggressively.