Trying to understand Summing Stacks V. Aux and VCA's

A summing stack is the equivalent of routing the outputs of a group of tracks to a bus and summing them on an Aux. On top of that routing, the summing stack offers the elegant stack feature, allowing you to close the track stack in the Tracks area, or to hide the individual channel strips in the Mixer. 

A VCA is different and isn't normally needed if you're using a summing stack. The VCA gives you a volume fader that offsets all the gain values inside the VCA group by the same amount, but doesn't affect the output routing of the tracks inside the VCA group. 

So if all your drums are in the summing stack, you don't need the VCA. 

Summing Stack: Its like busses/folder. You buss/folder keep tracks to it.

Aux: also a kind of buss but used mainly for sending fx. Up to you.

Vca: So you can control any groups/busses/tracks you want at the same time.

Each has their own use in a mix.

Summing Stack: Its like busses/folder. You buss/folder keep tracks to it.

Aux: also a kind of buss but used mainly for sending fx. Up to you.

It's worth pointing out that a summing stack is an Aux with all tracks routed to that aux (the audio routing is the same), the only difference is in what you call the "folder" functionality: the track "stack" part. 

Auxes and Busses are different animals. A bus is a virtual audio cable that routes audio from one channel strip to another. An Aux is a channel strip that has one audio input and one audio output and can process that audio signal. When sub-mixing, you're summing the output of multiple channel strips onto a bus, and set the input of an Aux to that bus in order to control and/or process the sub-mix.

 

 

Auxes and Busses are different animals. A bus is a virtual audio cable that routes audio from one channel strip to another. An Aux is a channel strip that has one audio input and one audio output and can process that audio signal. When sub-mixing, you're summing the output of multiple channel strips onto a bus, and set the input of an Aux to that bus in order to control and/or process the sub-mix.

Ever since Logic changed the nomenclature of what a "bus" means, I've been hard-pressed to find a reason to make busses visible to the user. They just seem like extra levels of indirection. If we route our drum tracks to Aux 1, why do we need to know that the digital signal is going through bus 5 in order to get there? I used to think busses were just depreciated entities that were being kept around for compatibility with older Logic files. What purpose do they serve now, from the user point of view?

Ever since Logic changed the nomenclature of what a "bus" means

I'm not sure what you mean? AFAIK Logic never changed that nomenclature. Busses have been used in analog circuitry way before Logic was created: https://en.wikipedia.org/wiki/Bus_(computing)

I've been hard-pressed to find a reason to make busses visible to the user. They just seem like extra levels of indirection. If we route our drum tracks to Aux 1, why do we need to know that the digital signal is going through bus 5 in order to get there? I used to think busses were just depreciated entities that were being kept around for compatibility with older Logic files. What purpose do they serve now, from the user point of view?

Oh I see, it seems like you're confusing busses (which are a general concept coming from the analog world, and which is faithfully modeled in Logic: a bus is a "virtual cable", just like a trace on a PC board: a means to transport an audio signal from one point to another, that's it.

On top of that Logic allows you to use (optional) Bus objects in order to process the audio signal present on the Bus. However Logic will not create those objects automatically unless you first manually create them in the MIDI Environment, which means that most people never use them. So I would say that 99.9% of Logic users never use Bus Objects. 

Those objects can still be useful in some rare situations, but in most cases they can be easily replaced by an Aux, even if that sometimes means using an extra Bus. For example if   I need a processed sub-mix signal on Bus X, I can first route all my tracks to Bus A, process that bus on the Aux that receives that Bus A, and route the output of that Aux to Bus X. You could save one bus by using a Bus object instead of an Aux to process the sub-mix, but in most cases that's not an issue. 

If memory serves, Logic formerly used the term "bus" to describe objects that we now call auxes. This follows the terminology of traditional hardware mixers, as you pointed out. 

At some point, the nomenclature switched so that we now use the term "aux" to refer to what in the mixer world would still typically be called busses. The shift seems to be from a naming an object after a physical mechanism on a piece of hardware to its conceptual role. No problem there. (For that matter, I assume it wasn't just a change of name, and that today's auxes are different in implementation than busses used to be.)

From your description, I'm sticking to my original theory. Busses are (mostly) redundant objects that are kept around to preserve functionality with older Logic sessions. I wouldn't mind that they exist except that we're constantly forced to see them. Whenever you route a channel to an aux, you're choosing a bus number as well. Since they appear to be more or less a depreciated feature, I wish they'd be swept under the rug entirely.

Auxes can serve other purposes than processing busses: they also serve to process  Intrument multi-ouputs (which are something different from busses, as far as Logic's audio routing implementation is concerned.

Similarly, busses (and therefore Bus objects, should you create some in the Environment) can serve other purposes than serving as inputs to Aux object: they can serve to route signal to plugins side chain inputs.

That's most probably why Logic differentiates Bus objects from Aux objects. Should you "merge" one concept with the other, you'd most probably get into compatibility issues.

IFAIK the only thing that changed over time (or the only thing I noticed) is that at some point, Logic started implementing a feature by which routing something to an unused bus automatically creates a new Aux channel with that bus as input into the Mixer. This is only for convenience and worklow efficiency purposes since Logic developpers assumed (rightly IMHO) that most of the time (but not necessarily all the time, as I show above) routing a signal to a new bus is done with the aim to further process that signal (thus the need for a new channel strip in the mixer, need that serves the Aux return). This is what may have started creating the confusion, but the two types of objects are not the same.

BTW, differentiating the two objects enables doing the following, which you would have no way to do (or at least not as efficiently) if you were "merging" the two concepts:

* Take a drum, e.g. kick drum, use that DRY signal to feed an FX side chain (e.g. Bass sidechain compression), and in parallel process that Kick with some EQ, FX, whatever, with only the WET signal being part of your mix...

* Logic's current way: route the output of the Kick to a bus, put all your EQ, FX, etc on the Aux return, and at the same time use the bus as input for sidechain.

* If you were to "merge" the two concepts you'd need two buses: one for "wetting" the Kick, the other (in parallel) for DRY sidechaining (plus you'd have to manually route the sidechain bus to "No Output" so that you don't hear it in the mix). Less efficient.

Yes, these are all excellent points. An aux is abstraction over busses and other signal routing entities that serve grouping functions. Better, faster, more bionic.

So all we need to do is get rid of busses...

All the more there are only 64 of them, these have become the bottleneck of many of my mixes these days.

Totally agree. We need at least 2x.

Okay, let me see if I've got the terminology entirely correct here ...

• A bus is a "sideways path" across the mixing board.  You can "send" signals to it from any channel strip – and/or, if you like, send the entire output of the strip to a bus.  Signals sent to a bus do not "go outside" unless a channel strip takes them there.  The signal that goes to the bus can be "tapped" from any one of three points in the audio-flow through any source strip.  You control how much signal is sent.  The send does not affect the output (if any) of the strip.

• An aux channel-strip is a strip that takes its input from a bus.  It "does something" to that input and then sends it somewhere – to another bus, or to Audio Out.  "The fact that it takes input from a bus is why we call it an Aux."

• Busses are always involved when dealing with aux channel-strips.  They're how inputs get into the strip and may also be how they get out.

• VCAs are a way to provide common volume control to all channel strips belonging to that VCA's "group."  This is not the same as the "Group" control that appears on every strip:  it is seen only when there are VCAs in the project.  (The signal routing if any in this case is not quite clear to me ...)

• Summing Stacks are a very cool and convenient way to route all of the members of the stack through a common bus and to an aux-strip that controls the entire group.  You can do the same thing "by hand," but in this case Logic is aware that you have thus grouped the tracks and so it allows you to expand or collapse the stack in the tracks view.  But, "how it works" is through a bus feeding an aux strip.

Is this entirely accurate?

Okay, let me see if I've got the terminology entirely correct here ...

 

• A bus is a "sideways path" across the mixing board.  You can "send" signals to it from any channel strip – and/or, if you like, send the entire output of the strip to a bus.  Signals sent to a bus do not "go outside" unless a channel strip takes them there.  The signal that goes to the bus can be "tapped" from any one of three points in the audio-flow through any source strip.  You control how much signal is sent.  The send does not affect the output (if any) of the strip.

• An aux channel-strip is a strip that takes its input from a bus.  It "does something" to that input and then sends it somewhere – to another bus, or to Audio Out.  "The fact that it takes input from a bus is why we call it an Aux."

• Busses are always involved when dealing with aux channel-strips.  They're how inputs get into the strip and may also be how they get out.

• VCAs are a way to provide common volume control to all channel strips belonging to that VCA's "group."  This is not the same as the "Group" control that appears on every strip:  it is seen only when there are VCAs in the project.  (The signal routing if any in this case is not quite clear to me ...)

• Summing Stacks are a very cool and convenient way to route all of the members of the stack through a common bus and to an aux-strip that controls the entire group.  You can do the same thing "by hand," but in this case Logic is aware that you have thus grouped the tracks and so it allows you to expand or collapse the stack in the tracks view.  But, "how it works" is through a bus feeding an aux strip.

 

Is this entirely accurate?

An Auxiliary channel strip can also take its input directly from your audio interface's inputs.

As for VCA, the signal routing of the individual channel strips does not change, the VCA fader just provides an offset to each channel strip's gain value.

MikeRobinson, some minor additions on top of David's:

* Auxes can also take their input from the various outputs of multi-outs instruments

* As a consequence, buses are not *Always*, by *Most often* involved when dealing with Aux channel strips.

* The nice thing about Summing stacks is that you can collapse:expend them in the Mixer too (as well as in the Tracks view - by default both views will collapse/expand synchronously);

* Actually, the same is true of Folder stacks. A folder stack (which you don't mention), is a group of tracks all controlled by the same VCA, and setup as such so that they offer the same collapse/expand feature as Summing stacks. Contrary to Summing stacks, no Bus routing and Aux is involved, the only thing is that the VCA provides a level offset for all volume faders of the Folder stack tracks (which retain an individual routing of their own).

* Following the analogy with Summing stacks, you can link tracks (channel strips actually) to a VCA "by hand" (by selecting various channel strips in the Mixer and do Options > Create New VCA for Selected Channel Strips), but in that case you d'on't have the collapse/expand feature.

* In other words, Summing stacks are a Logic-aware advanced version of common bus routing of various tracks with an Aux, offering collapse:expend functionality in Tracks view and Mixer view and, similarly, Folder stacks are a Logic-aware advanced version of common VCA control of various tracks, offering the same collapse/expand functionality.

* You can gather Summing stacks in a Folder stack, but not the other way around, and you cannot gather Summing stacks into other Summing Stacks or Folder stacks into other Folder stacks (which restrictions are a pity because the "by hand" ways offer the possibility to create such several-depths configurations).

Hey so I've been using the stacks a lot and I have some questions. 

1. Is it okay to place a summing stack inside a folder stack? If so does it affect the sound and it what ways?

2. Can I put multiple summing stacks inside a folder stack?

3. Are there situations I shouldn't do this?

Thanks 

Incredibly helpful discussion. Makes perfect sense now. You just took me to a new level.

One question. Is Automation of volume equivalent on all the stack and vca options? In other words, should you choose one option over another for this one function?

All the more there are only 64 of them, these have become the bottleneck of many of my mixes these days.

 

Totally agree. We need at least 2x.

I'm just glad they went 4x.

Hey Eric,

Chiming in here after quite a while of hard work and very little time to devote to this wonderful forum (I've not even taken the time yet to update to 10.3.2, that must tell something...).

My turn to totally agree with you!

Cheers.

It's lovely I tell ya!

This and the ability to protect busses from being auto assigned is pure gold.