I Don't "Get" VCA Channels in DAWs - Can Someone Explain?

[Anderton]

Like the thread title says. Pro Tools has 'em, Studio One has 'em, Cakewalk forum people wish it had 'em...but I don't see what makes people get so excited about them.

 

As far as I can tell, the basic deal is that a VCA channel isn't like an audio channel, but more like a control signal generator. As such, one advantage is that you can use it to create multiple automation lanes in multiple audio tracks at the same time. I also know that the most common cited attributes are that you can offset automation easily, and that if you have a group being controlled by a fader, the amount of post-fader reverb stays the same when you bring the group down because the fader itself isn't changing.

 

But is that all there is to it? It really doesn't seem all that amazing. You can do the same thing for reverb by sending the sends to a reverb send bus, which then has a send to the reverb. So if you group the drums' audio bus fader with the drums' reverb send bus, you can bring down the reverb as you bring down the drums, without affecting anything else that goes to the reverb.

 

As to automation offset, most automation lets you bring an entire automation envelope up or down. Cakewalk even has an offset mode where the faders control level irrespective of the automation envelope. And I guess writing automation to a bunch of tracks at the same time is useful, but if they're bused, why not write automation to the bus?

 

I must be missing something...

[Mike Rivers]

Like the thread title says. Pro Tools has 'em, Studio One has 'em, Cakewalk forum people wish it had 'em...but I don't see what makes people get so excited about them.

 

I don't either. Is there a new definition of a mixer VCA channel? The way these newfangled software designers don't know their history, I wouldn't be surprised if it's an old name borrowed to attach to a new feature. But if it's not an emulation of VCAs in an analog console, then I don't know what to say.

 

As far as I can tell, the basic deal is that a VCA channel isn't like an audio channel, but more like a control signal generator. As such, one advantage is that you can use it to create multiple automation lanes in multiple audio tracks at the same time.

 

That's a kind of complicated way of thinking of it. In an analog console with VCA automation, there are usually several VCA groups available. You assign a few channels to the same VCA group, assign one channel to be the group master, and then all the other channels in the group follow that fader. Functionally, it's like assigning channels to a subgroup, or, with panning, to a pair of subgroups, un-assigning those channels to the main mix, and feeding the subgroup to the main mix instead. DAWs tend to befuzzlate "track" and "channel" as it's convenient, but I've gotten over that. I envision that a VCA "channel" is like the master fader of a VCA automation group, and of course you can write automation to that track. And you can probably write automation to individual tracks within that VCA group, too, and still use a master fader or, if you will, automation track, to control the level of the whole shebang.

 

But is that all there is to it? It really doesn't seem all that amazing. You can do the same thing for reverb by sending the sends to a reverb send bus, which then has a send to the reverb. So if you group the drums' audio bus fader with the drums' reverb send bus, you can bring down the reverb as you bring down the drums, without affecting anything else that goes to the reverb.

 

Alternatively, you could put the drum reverb bus fader on the same VCA group as the drum mix (or whatever of the drums you're sending to that reverb) and it would be like a post-fader send.

 

VCA groups were mostly used for muting, like to mute the background vocals when you don't need them. This was more important when you wanted to get rid of the tape hiss on a track that wasn't part of the mix. But, also, it's used for group fades.

 

I must be missing something...

 

More likely, I am. It's certainly a feature that I would have expected to be available in just about any DAW, but users have had a long time to either get used to doing group fader moves and mutes some other way that the software designers can make something old new again and call it an upgrade or update.

 

[zeronyne]

Are they using VCA in terms of how modular synths do it? (And yes, I know they are the same thing in the literal sense). I don't quite get it except it's a lot more skeuomorphic compared to drawing in the automation, which always seemed a lot more convenient. But then again, the whole concept of a mixer inside a DAW is a nod to how people "used" to do things. I think you are right, Craig, and I don't think you are missing anything. Maybe the fans of dedicated VCA channels never got into automation or modulation outside of the mixing board paradigm.

[Mike Rivers]

Maybe the fans of dedicated VCA channels never got into automation or modulation outside of the mixing board paradigm.

 

That's probably me, though I have no idea of what you mean by that.

 

Within the mixing console paradigm, a VCA is a circuit, often implemented on a chip, and the fader doesn't carry the audio signal, it adjusts the control voltage going to the VCA, which carries the audio. The alternative is the motorized fader, that does carry the audio signal, and the control voltage drives the motor that moves the position. The same control voltage can be applied to multiple faders, or multiple VCAs, and that that's how you get fader groups. The advantage of a moving fader automation system is that the fader knob serves as an indicator to give you a visual idea of the channel level. This is easy to implement in a DAW that uses a mixing console paradigm for its control panel. With VCAs, the only time the faders move is when you move them. If you have several VCAs grouped to a single master fader, when you move that fader, the levels on the slave channels change, but their fader positions don't.

 

But just to be sure I know what I'm talking about, does VCA mean Voltage Controlled Attenuator? Or does it stand for something else that might be meaningful to whatever you use it for.

 

I recognize that with a DAW, "Voltage" is represented by a digital word, as is the "Attenuation," but the functions carry through from analog to digital. Modular synths, and even non-modular synths, use(d) a control voltage, which is actually a voltage, to control many different things - pitch, amplitude (volume), modulation frequency and depth, and waveform, to name a few.

 

[S_Gould]

I'm sure Dr. Anderton will be along to explain that in the world of synthesizers, VCA means Voltage Controlled Amplifier. I doubt that it woiuld be used differently just because the circuit is in a mixer.

[Anderton]

Well here's the thing, digital mixers do borrow that term, although of course it's not a real VCA. But that begs the question of what made VCA faders so important in the hardware digital consoles that preceded virtual mixers, what elements were maintained, and which elements were enhanced in the transition to software. I'm starting to think there's not a lot of "there" there, unless you're working with projects that have lots of tracks, many of which are interrelated (e.g., string sections, drum kits, choirs, and the like).

[Theo Verelst]

I don't know about the software packages containing such a fancy named fader ganging, but a mixer with VCA's could have various reasons, the main simple one being automation of a channel strip slider or a (sub) group slider. An advantage of a VCA in strip could be the adaptation of the gain level through automation such that the signal levels from an input could be adjusted to the mixer line by a (DC) control voltage, maybe coming from a computer+DAC.

 

From the analogue versus digital point of view extra distorting VCA blocks can be justified in the analog domain when playing back digital with some effect like LFO or envelopes from e.g. compressor signals.

 

Maybe there was concern about automating tracks in a DAW that fast moving software sliders generate clicks or audible slide curves on the digital material (which certainly can be true). In the most advanced implementation of a software simulated VCA, there would be purity in the VCA control input signal simulation, and consideration for the sampling errors that come from especially quick amplitude changes.

 

TV

[Mike Rivers]

Well here's the thing, digital mixers do borrow that term, although of course it's not a real VCA. But that begs the question of what made VCA faders so important in the hardware digital consoles that preceded virtual mixers, what elements were maintained, and which elements were enhanced in the transition to software.

 

Well, the reason why they were put in analog consoles in the first place was so that you could have automation without the cost of moving faders. Grouping for manual control was just the sideshow, but useful none the less, because it saved passing channels through another stage (subgroup) of the console on the way to the main mix. The bugaboo with VCAs is that early ones had some leakage of the control voltage into the signal path, resulting in some unwanted modulation of the channel audio when they were moved too fast. Of course in software, that's not a problem as long as the math is accurate. But with software you don't really need to assign tracks to buses if you just want to control their level simultaneously, you just multiply them by the same number, with that number generated by moving a fader. I guess that's an enhancement.

 

Another enhancement is that you can create a graphic of the effective fader position in the software mixing console view. This served the "indicator" function of a moving fader. This can be implemented in a couple of ways. The classic VCA hardware fader had a pair of LEDs next to the fader that would tell you if the physical fader was above or below what the actual gain setting is. Most automation systems would allow you to edit automation by engaging the Write mode and moving the fader, but to avoid sudden changes in level, the new automation data wasn't written until you crossed the "null" point with the fader knob. With a virtual indicator of the channel gain setting, it's easier than moving the fader until both LEDs went out.

 

I'm starting to think there's not a lot of "there" there, unless you're working with projects that have lots of tracks, many of which are interrelated (e.g., string sections, drum kits, choirs, and the like).

 

Well, yeah. But doesn't everyone work with too many tracks already? I guess it could be helpful if you have 12 stacked guitar tracks all playing the same thing slightly out of sync and out of tune and with a different amp simulator on each one. It's really just like clicking on a bunch of tracks, assigning them to a control group, and putting a handle on it. I suppose one advantage of calling a "control group" a "VCA" is to trick old farts like me into thinking "Hey, this works just like my old API."

 

[Franknputer]

My guess is that it's around master automation (this is off the top of my head, so take it with a grain of salt..). If you gang the faders then sure, you can move a group in concert (no pun intended). But what if you want to change the mix within that group during the song?

 

Imagine this: you have a group of drum tracks, and you want to ride the toms up during fills and then pull them back down. If the channels are grouped, (I believe) this would have the effect of simply pushing the entire kit up, and you couldn't automate the toms independently. However, if the channels are assigned to a virtual VCA then you can automate the tom pushes because the channels are still independent, and then you can automate the overall kit (to push up the drums for the chorus, for example) using the VCA.