Pro Tools VCAs and Trim Automation to Make Mixing Easier

Automation Basics

While compression can be a powerful creative tool, over-compression of signals during recording or mixing can become a “lazy” way of maintaining balance throughout playback of a song. If all of the dynamic volume changes of the sources are removed or highly reduced through compression, mixing becomes largely a set-and-forget process of balancing instruments and applying processing/effects. This however, does not necessarily result in the most interesting mixes, and can often make a performance sound flat or dull.

Through effective mix automation, this phenomena can be avoided and the precious micro and maco-dynamics of a source can be preserved, resulting in an end product with so much more life than its over-compressed counterpart. Taking the time to actually “ride” levels throughout a song turns a mix into a kind of performance, allowing each component to remained balanced despite wide dynamic changes, while preserving the integrity of the original signal.

While many music styles and sources can actually benefit from effective (and often high) compression, the resulting “sound” should be a creative choice, not a by-product of shortcuts to make the mixing process faster, or lack of knowledge or technique.

Automation can easily become as much as 50% of the total time that I spend on a mix, even in simple fader/mute console automation systems.


The power of modern DAW systems gives you many more options to manipulate the performance of a mix in real-time and by opening up more possibilities, can serve to increase the time spent on this crucial step.

When time is money, I obviously have a motivation to get things done quickly, but DAW mixing speeds up so many of our process to a degree that it should allow us to spend more time to get these critical finishing touches “right”.

Analog Console Automation

Analog recording consoles have featured two types of fader automation systems: VCA and moving fader.

VCA stands for voltage-controlled-amplifier. In a VCA fader, the signal does not pass through the analog fader circuit directly, but rather a control voltage. The control voltage (CV) is trimmed by the fader and fed to the CV input of the VCA, which in -turn adjusts the gain accordingly. The CV is also read and stored by the automation computer and, during automation playback, fed to the CV input of the VCA, in lieu of the fader CV output.

With a VCA-based fader automation you will never see the faders move but your automation moves will still playback in real-time. You may be able to monitor “virtual” fader positions via console metering, or computer interface, and even match original fader levels through delta indicators on the mixing console.

A moving (or motorized) fader system is just what its name implies. A position sensor and linear motor are attached to a traditional linear fader. Signal passes through the linear fader, just as with a non-automated fader, but the console computer stores the real-time output of the position sensor. The electronics of the position sensor circuit are very similar to VCA based automation systems but, during playback, the CV signals control the position/movement of the linear motor (which in turn moves the fader) instead of a VCA circuit.

Many engineers consider the motorized system superior to the VCA system not because of the motion of the fader, but due to the distortion inherent to a VCA circuit. Some very successful mixing engineers, however, have crafted this distortion characteristic into a part of their own signature “sound”.

In either case, the console would be synchronized to the multi-track using SMPTE/EBU time-code to allow synchronized record and playback of automation moves.

SSL 4000 G/G+ Automation

Early automation, especially moving fader systems could be quite expensive, so many console manufacturers included it only as an option or third-party systems could be integrated if a studio wished. The SSL 4000 G/G+ series consoles were arguably the first production consoles to feature an integrated console computer and automation system, the G bearing a VCA-based system and the G+ including “Ultimation”, a hybrid VCA and moving fader system.

The advantage of the Ultimation hybrid system containing a touch-sensitive fader controlling both VCA and moving fader circuits, was the ability to perform both Absolute and Trim mode recording of automation in real-time, while monitoring a previous automation “pass”.

Absolute-mode automation overwrites any existing automation from a prior pass. In this manner, moves can be re-recorded until signals are balanced perfectly throughout playback. An example of this would be “riding the vocal”, wherein the vocal fader is hand manipulated from phrase-to-phrase, word-to-word, and sometimes even syllable-to-syllable to ensure that it stays perfectly leveled in the mix; neither too quiet, nor too loud.

Trim-mode automation adds to or subtracts from pre-recorded automation. With a VCA-based automation system, the console computer could simultaneously play back previously recorded automation moves and trim them based on current dynamic values, re-recording a new combined automation pass. Even trim-based automation always has to start with at least one Absolute-pass in which baseline levels (either static or changing) are recorded from the beginning to end of a mix.

With SSL Ultimation system, containing both moving-fader and VCA-based automation circuitry, a mixing engineer could harness the best features of each system: the real-time trim-based automation featured in VCA based systems, and the sonic characteristics of a moving fader system during playback.

A mix could be built up of many passes using each technique as appropriate and played back through the moving fader system.

The SSL G/G+ also featured a handful of VCA group-masters in the center section of the console that allowed multiple faders on the board to be controlled by a single master. The VCA group-masters passed no signal, their only purpose is to control groups of faders from the center section. Even the VCA group-masters could be assigned to another master, a technique known as cascading groups, to allow individual control of a sub-group, with a master controlling additional faders or sub-groups (i.e, your Lead fader and BG Vocal group may be controlled by a single Vocal group).

DAW Automation

Modern digital audio workstations’ and digital consoles’ mixing systems have been designed, largely, to emulate the workflow of these traditional analog desks. While DAWs and digital consoles, and some very high-end analog desk, allow many more features (pans, sends, inserts, eq and dynamics) to be automated, terminology and practices in absolute/trim-mode and VCA/moving fader systems are still prevalent in these systems today and work, basically, the same. The prevalent example in this article will be Pro Tools, though it’s worth noting that many other DAW’s have similar functioning features.

VCA Masters in Pro Tools


Pro Tools New Track Dialog – Click to Expand

Pro Tools 7.2 introduced an array of automation and operation features that were intended to help engineers familiar with large-format analog desks to make the transition to working in Pro Tools and, especially, the Avid/Digidesign ICON Worksurfaces. One of these features included the addition of VCA Masters as a track option in the New Tracks dialog.


The careful selection configuration of Mix Groups and VCA Masters can make the task of both balancing and automating your mix much easier.

How and Why to Configure VCA Masters

A VCA Master in Pro Tools is capable of controlling any Mix Group. To create a VCA Master, utilize the New Tracks dialog. When organizing my mixing session file, I will usually generate 8-12 right up front, and Disable/Hide any that are unnecessary. Assigning a Mix Group to a VCA Master can be accomplished in one of two ways:


Pro Tools VCA Assignment – Click to Expand

If you have existing Mix Groups that you wish to assign VCA Masters to, you can select where an Audio Track would normally display it’s Track Output (this will read “No Group” for an unassigned VCA Master), and select the appropriate Mix Group from the resulting menu.




When creating new, or modifying (7.3 or later), Mix Groups, you can select a VCA Master from the drop down menu indicated by “VCA.”


Pro Tools Modify Groups Dialog – Click to Expand

You can now alter not only Volume, but Mute, Solo, Record and Input states, for the entire Group utilizing the VCA Master. You can also automate both Volume and Mute from the VCA Master as you would with any other track type, resulting in automation of all tracks associated with the VCA Master (assigned to the corresponding Mix Group).

The advantage of creating a VCA Master over just leaving it as a traditional Mix Group, is that the individual channels can be adjusted and automated separately from the VCA Master without affecting the other tracks in the group.

Not only do you no longer have to hold Ctrl (on Mac, Alt on Windows) while making adjustments to individual group members but, more importantly, you can still adjust individual track states even after automation is written to the group master. With traditional channel automation, once automation has been written to the Volume Automation Playlist, you must either Trim or Edit the written automation in order to change over-all mix volume.

By writing automation to the VCA Masters wherever it is feasible, you speed up your mixing process by allowing yourself to retain the ability to alter individual members of the group simply by grabbing a fader or control.

Once automation has been written to a VCA Master it can be composited (combined) with Volume automation on it’s member tracks by selecting Coalesce VCA Master Automation from the Tracks menu, or by right-clicking the track name and selecting it from the context menu. This will write the resulting automation to the tracks, clear the VCA Master playlist, and set the VCA fader volume to Unity.

When mixing on a worksurface like the Avid ICON, I’ll typically either create a Custom Fader Group or Nudge/Bank the faders so my VCA Masters appear in the most conveniently located group of channels (typically, just left of the center section). Once configured, more than 50% of my Volume Automation will occur on the VCA Master.

This means less time editing points and lines on a track and more time listening.

Cascading VCA Groups in Pro Tools


A screenshot showing multiple VCAs and Audio Tracks (hi-hat) assigned to a single VCA Group – Click to Expand

Cascading VCA groups (creating sub-groups controlled by larger groups) can easily be accomplished. VCA Masters, like any other track type, can be assigned to Mix Groups. By simply assigning a VCA Master to a mix group controlled by another VCA Master, you have defined a sub-group.




An example of where I use this would be when dealing with multi-mic’ed drum kits. I may have multiple Kick, Snare, Tom, Overhead or Room microphones, and I will create a Mix group so that each can controlled by a VCA Master. I will then assign each VCA Master, along with any “orphan” drum tracks such as Hi-hats or other spot mics, to a single Drum Mix group which has it’s own VCA Master.

Using Trim Automation in Pro Tools

Another advancement of Pro Tools 7.2 was the ability to store and edit Volume Trim automation in a separate Playlist from “absolute” Volume automation. If you click your playlist drop-down, you will now see separate Volume and Volume Trim playlists.

When viewing the Volume playlist, the absolute Volume automation will appear in black with editing points/handles as normal. If the fader has been adjusted in Trim Automation mode, or even changed while Trim Automation mode is enabled, there will also be a blue line indicating the resulting automation that will occur on play back, a composite of Trim Volume and absolute Volume.

When viewing the Volume Trim playlist, the Trim Volume automation will appear in yellow with editing points/handles. Likewise, the resulting composite of Trim Volume and absolute Volume will appear in blue.

Keeping Trim Automation and Volume Automation Separate

A trick that I use to speed up my mix is to keep Volume and Volume Trim automation separate, for the most part, and perform most of my dynamic automation in the Volume Trim playlist. This means always selecting “Trim” when automating a fader volume.


Pro Tools Mix Preferences – Click to Expand

To keep these playlists separate, you must disable Pro Tools’ default preference to automatically coalesce (combine) automation playlists. This is done through the Automation section of the Mixing Preferences, by changing the Coalesce Trim Automation Options radio button to Manual. While Pro Tools will play back automation as a composite playlist, you must manually coalesce your Trim and absolute Volume playlists to commit your changes to a single Volume playlist.

While I’m here, I usually adjust the AutoMatch Time to a relatively minimal value (50-100ms) and set the After Write Pass, Switch To option to Touch. Even though I often elect not to disarm a fader’s automation state from “Write” to “Off” after an absolute pass the channel will remain in Read mode until I touch and move a fader, at which point it will begin writing automation to either the Volume Trim (if Trim is enabled) or Volume automation playlist. As soon as I release the fader, it will return quickly (but not instantly) to it’s former recorded position.

I use the Write to End or Write to Punch commands in the Auto Enable window to make broader changes without playing through a long section.

The advantage of writing all of your early automation to your Volume Trim playlist is that, while Pro Tools will always play back your Volume Trim automation when in Read, Touch, or , you can still alter your overall volume for the track by simply grabbing the fader and moving it when in a standard mixing mode. This means you can perform vocal rides throughout a song, but still adjust the overall level of the track simply by moving the fader, with Trim disabled.

Performing Trim “Style” Moves

If you want to perform a Trim style change when using this technique (i.e. increasing the volume of just the choruses, while maintaining the word-to-word automation, of your vocal track) you have three options:


Pro Tools Coalesce Automation in the Tracks Menu – Click to Expand

You may write your Trim style automation to the absolute Volume playlist, or, you may use the Coalesce Trim Automation command to instruct Pro Tools to combine your absolute Volume and Volume Trim automation into a single Volume playlist. Either case bears one disadvantage: you can no longer independently control absolute Volume and Volume Trim without editing or recording additional automation.


The third option, and one I use often, is to use Pro Tools 10’s Clip Gain feature to make fixed changes to level. It should be noted that these changes will precede any channel processing, so it should only be used for subtle, broad changes.

Happy Mixing!

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