VCA masters (Pro Tools with Complete Production Toolkit or Pro tools HD) are a great tool for mixing large sessions in the box, especially if you do not have access to a control surface. The term VCA which stands for Voltage Controlled Amplifier comes from the analog world, where consoles would have these VCAs that could control multiple signals together and also maintain the relative balance between the signals. So if you had a group of 6-8 tracks which represent an entire drum-kit (kick, snare, toms, hi-hat etc.) where each track is set at a different level, you could control all the tracks with just one VCA, while maintaining the offsets between them. Now you may think that the same can be achieved with simple groups or Aux tracks in Pro Tools but there is so much more to VCAs and I'm going to highlight some of their features in this article.
Creating VCA Masters
Go to Track > New and in the dialog box that follows, you can choose to create a VCA Master. You will notice that the option for creating a mono, stereo, LCR, quad etc. is not available. This is because VCAs are not actual tracks, they just control other tracks. So the track type is defined by the tracks it is controlling. This also means that it does not take up any voices, so feel free to add as many VCA Masters as you need. The maximum number of useable VCAs is defined by the maximum number of groups which is 104.
Creating VCA Groups
Once the VCA Master have been created, they need to be assigned to groups in order for them to control the 'slave' tracks. Select a few tracks from your session that you would like to control with a VCA and group them by going to Track > Group. In the dialog box, give the group an appropriate name and uncheck 'Follow Globals'. It will still work with this option checked but it's best to leave the global settings for regular groups. Do make sure that the group is either a 'Mix' or 'Mix/Edit' one. If you make the group an Edit group it won't work as a VCA group. If you have already created the VCA Master, the group can be assigned to one by choosing it from the VCA option in this dialog box.
The VCA master should now be simultaneously controlling the faders of the slave tracks in the group and you can still control the individual slave tracks independently by just moving its fader directly. So you kinda get the best of both worlds which would not be possible with regular groups. In fact, the group doesn't even have to be ON in the Groups tab for it to work. Once it's assigned to a VCA, it functions irrespective of its ON/OFF state. The ON/OFF state is applicable mainly for regular groups.
If you go to the Groups Tab, right-click on a group name and select Modify. You will see the same window you saw while creating the group. You will notice the 'Edit' option is now greyed out and if you click on Attributes you will see that Volume and Mute are also greyed out (if 'Follow Globals' is unchecked). This is because the VCA Master will control those parameters either way. You can enable more parameters in the group but the VCA Master will not control them. The VCA Master only controls Volume, Mute, Solo, Input Monitoring and Record Enable. The Input Monitoring and Record Enable will only be controlled by the VCA Master for the tracks that already have those parameters enabled. So if a kick drum & snare track is record enabled in a group, its VCA master's Record Enable switch will work on just these two tracks ignoring any other tracks in the group. To force all the tracks in a VCA group to be controlled by the VCA master for Input Monitoring and Record Enable, Option/Alt click on the VCA master's Input Monitoring or Record Enable switch respectively.
Metering on VCA Masters
It may seem that the VCA Master's meter would show the sum of all the slave tracks but instead it actually shows the highest level occurring in the group. So the meter display may jump between tracks depending on which track is loudest at any time. There is no indication of which slave track is currently being displayed.
The number of meters on the VCA Master depends on the type of slave tracks in the group. For example if the group has all stereo tracks, the VCA Master will have two meters. If the group has different type of tracks(stereo & mono) the VCA Master will just have one meter.
Automation with VCA Masters
Any automation written on a VCA master will be reflected on the slave tracks. As shown in the screen shot below, automation was recorded on the VCA Master and the 5 slave tracks have the same automation reflected in their volume playlist with the blue line.
Another handy feature is to transfer this automation to the slave tracks permanently and thus reset the VCA back to unity for further automation. To do this, right-click on the name of the VCA Master and choose 'Coalesce VCA Master Automation'. In the image below, the same VCA Master track was coalesced to its 5 slave tracks. Notice the slave tracks no longer have the blue line representing the volume automation.
If automation is written directly on any one slave track, it will take precedence and ignore any existing automation from the VCA Master track but what will happen is that the main automation playlist (black line) will compensate for the new automation written (blue line). In the image below, automation was written directly to the slave track Vox3 which is represented by the blue line, but since there was existing automation on the track via the VCA Master, Pro Tools compensated for it by riding the main volume playlist (black line) in the opposite direction.
If this doesn't make sense, just ignore the black line and focus on the blue line as that is the resulting volume automation. To confirm this you can try the 'Coalesce VCA Master Automation' on the VCA Master and you will see that the slave track which had its own automation still maintains the exact same automation, just that it is now represented on the main automation playlist (black line).