Understanding Busses, Groups and VCA
 

Hi,
I'm getting to know Pro Tools and like it so far.
I have trouble understanding the difference between a bus, a group and a VCA-fader.
1. Is it correct that a VCA-fader only controls other tracks without the signal actually running through it?
2. In a video, a guy explained how to create group tracks via aux input channels. He created an aux input track, then he assigend the tracks he wanted to be on it to a bus, then he selected that bus as input on the aux input track.
In a different video, another guy just selected the aux input track as output on the tracks he wanted on the aux input track, without going via a bus.
Does that make any difference?

Re: Understanding Busses, Groups and VCA
 

Yes, VCAs are just remote controls for a group of channels that are assigned to the VCA group master fader. As such the VCA group master fader only controls the POST FADE out put of the channel which are assigned to it. When pushing the VCA group master fader up, it increases the levels of those channels which are grouped to it, while maintaining their levels relative to each other. There is no audio that passes through the VCA group master fader.

Setting up channel groups is similar to VCAs, except that you don't get the VCA group master fader and you have to ungroup the channels to make changes to their levels relative to each other.

In live sound consoles (where VCAs (or DCAs as some manufacturers call them) originated) you can automate the channels that are assigned to each VCA group on a scene by scene basis. So in one scene VCA 1 might have just the lead vocal in it, in the next scene, VCA 1 might have another singer, and the channel that WAS on VCA 1 previously may now be on VCA 3 as part of the female chorus. It's kind of complicated, but Protools doesn't provide for scene memories, so they don't really get the full value of VCA automation.


There are multiple ways to skin a cat. Depending on what your goal is and what workflow you are comfortable with.

Bussing a channel to another channel, such as an AUX send allows you to send the signal from that channel to the AUX while still outputing it to the main output to which it is assigned. This is often used for sending a channel (or portion of) to an effects processor such as reverb, when you still want to hear the main output of the channel and be able to mix in the reverb at a different level.

Sending a channel to a different output is just that. Perhaps you want the channel assigned to only your rear speakers, or to the subwoofer, or maybe only to fold back monitors. Changing the main out put of a channel will take it out of the other output completely.

Re: Understanding Busses, Groups and VCA
 

JC did a great job, but I wanted to offer a little history and zero in on the term "VCA" and what it really refers to. What we have in Pro Tools is really a "virtual VCA master" and here's why. In an analog console(with VCA's) every channel has a VCA(Voltage Controlled Amplifier) that raises and lowers the volume of that channel. Each VCA is controlled by the channel's fader because the fader controls a voltage(0-10vDC) that feeds the VCA(so the fader actually passes no audio, only DC voltage). The VCA Master faders simply over-ride the voltage of the channel VCA's that are assigned to that master. :D