Auxes, buses, sends, returns, VCAs, groups, subgroups, and many more terms make up the wide lexicon of audio technology. When learning about music and audio production, the glossary of terms can be overwhelming, and what's worse is that many terms are used interchangeably. Let's consider these related terms and their definitions to help you keep up with the learning process.\n\n\n\nWhat are the differences between buses, groups, auxiliary sends\/returns and VCAs in audio technology? Here are the key differences, in point form:\n\n\n\n\nBus: any kind of audio signal path that allows the combination or "summing" of different signals to be routed\/processed together.\n\n\n\nSubgroup: a grouping of instruments or tracks that are mixed or inserted into the "main" mix as a composite signal.\n\n\n\nAuxiliary track: a type of bus for creating auxiliary mixes or common parallel processing.\n\n\n\nAuxiliary send: the aux bus that feeds the auxiliary effects and processors.\n\n\n\nAuxiliary return: the mixer channel fed by the auxiliary effects and processors' output.\n\n\n\nVCA (voltage-controlled amplifier): a voltage control source that acts as a master control over the volume levels of the channels in the VCA group. VCAs do not pass audio.\n\n\n\nGroup: the linking of certain user-defined functions, notably level, between tracks (other options include editing, automation, alternative\/playlist select, panning, solo, mute, and record arm).\n\n\n\n\nThese simple definitions will give you a solid idea of what these terms mean. However, because some words are often used interchangeably and may be used differently between DAWs and hardware mixing consoles, we should dive deeper into their full definitions. That's exactly what we'll do in this article.\n\n\n\n\n\n\n\nA Primer On Signal Flow\n\n\n\nTo understand buses, subgroups, auxiliary tracks, sends, returns, VCAs and groups, we should understand signal flow.\n\n\n\nAs the name would suggest, signal flow refers to the flow of an audio signal, whether we're going live, recording or mixing.\n\n\n\nWhere does the audio signal originate, and where does it end? Where does the signal go between its start and end points? What inputs and outputs does the signal goes through, and how is the signal carried between each output and input? There are the questions of signal flow.\n\n\n\nIn analog systems, we actually have electric current flowing through electronic devices. In digital audio, the same idea applies, except it's based in a digital representation of audio.\n\n\n\nLet's consider the signal flow of an electric guitar being recorded into a mixing console as a related example:\n\n\n\n\nThe guitar string vibrates (sound, not audio).\n\n\n\nThe pickup(s) convert the vibrating magnetic string into an electric current (audio signal).\n\n\n\nThe audio signal passes through any volume, EQ, etc., potentiometers on the electric guitar.\n\n\n\nThe audio leaves the guitar output and travels through the patch cable to the amplifier input.\n\n\n\nUpon arriving at the amplifier input, the signal is amplified through tubes, transistors, transformers, digital modelling, etc.\n\n\n\nFrom the amplifier output, the signal travels to the cabinet speaker input.\n\n\n\nThe speaker produces sound to recreate the audio (sound, not audio).\n\n\n\nA microphone picks up the sound from the cabinet.\n\n\n\nThe microphone outputs the signal through an XLR cable to a mic input at the mixer.\n\n\n\nThe mixer applies gain at the mix input, and the signal can be processed by any processes on the designated channel (EQ, compression).\n\n\n\nThe signal is sent through the mixer (the topic of this article), eventually to the mix bus and the output of the mixer.\n\n\n\nThe signal is sent to the input of a power amplifier, amplified and outputted through speaker cables to the inputs of a pair of studio monitors, which produce sound representing the audio.\n\n\n\n\nNote that sound is technically not part of signal flow. I just wanted to give a complex example to give you an idea.\n\n\n\nRelated article: What Is The Difference Between Sound And Audio?\n\n\n\nAnd that's only touching the surface. Plenty of signal flow and routing can be done inside the mixer (or the digital audio workstation, for that matter). Signals can be combined, split, recombined and resplit in a multitude of ways, which is what we'll be discussing shortly.\n\n\n\nIn this article, we'll examine several of the most popular routing options for signal flow within mixers, notably buses, subgroups, auxiliary tracks (including sends and returns), VCAs and groups.\n\n\n\nTo set ourselves up for success, let's quickly go over the start and end points of a typical mixer.\n\n\n\nThe audio signals in a mixer generally come in on a channel. A channel is designed to accept microphones, line-level devices such as amplifiers, preamps, signal processors (EQs, compressors, etc.), and\/or direct instrument-level signals.\n\n\n\nThe more channels a mixer has, the more audio signal can be connected and routed through it. This is true of recorded signals, live signals, auxiliary "return" channels, subgroup mix channels, and more.\n\n\n\nIn terms of semantics, channels are often called "tracks" in mixing.\n\n\n\nThe output of each channel is typically automatically routed to the main stereo output of the mixer (often referred to as the mix bus). The bus, which sums signals together, combines all the channels together to output them properly in the main outputs.\n\n\n\nEach channel typically also has a few auxiliary sends, which effectively split the audio to send it to both the channel output and to a separate auxiliary track channel. The auxiliary track\/channel, like the other channels, typically has its output routed to the mix bus\/main stereo output.\n\n\n\nSome mixers, and nearly all digital audio workstations, will have several bus options for the channel outputs, which we can use to group similar channels together into submixes for more streamlined mixing. It's generally easier to process many tracks' audio at once through a subgroup than processing each track\/channel individually.\n\n\n\nA VCA (voltage-controlled amplifier) isn't a channel and doesn't actually affect the routing within a mixer. Rather, it can be used to control the gain of multiple channels at once on a single fader. No audio passes through the VCA as it's not a channel but simply a fader that uses a control voltage (or a digital representation of a control voltage) to alter the gain of multiple tracks at once.\n\n\n\nThe term "group" in modern digital audio workstations has little to do with routing. It generally refers to linking parameters between multiple channels for easier mixing and editing. For example, we can group all the guitar tracks together and set up the group so that moving one fader moves all the faders, editing the audio at a certain playhead position edits all the audio at that playhead position, sending one track to a certain auxiliary track sends all the tracks to that auxiliary track, and so on.\n\n\n\nOtherwise, the term "group" is synonymous with "subgroup".\n\n\n\nThe terminology can be different depending on the mixer or the DAW. Although I'll do my best to generalize throughout this article, your specific equipment and software may put slightly different labels on what we're about to discuss.\n\n\n\nSo with that long primer, let's get into buses, subgroups, aux tracks\/sends\/returns, VCAs and groups to better understand their roles in mixing, recording and audio production more broadly.\n\n\n\nIf you'd like an in-depth discussion on routing, check out my detailed video below:\n\n\n\n\nhttps:\/\/youtu.be\/M5HbmWpaPXI\n\n\n\n\n\n\n\n\n\n\nWhat Is A Bus?\n\n\n\nA bus, in audio, is a signal path that can carry audio from multiple sources from one place to another. Buses, themselves, are not channels. Rather they are signal paths than can connect channels. A track\/channel output or its auxiliary send can be set to a specific bus (Bus 1, for example), and a subgroup or auxiliary track's input can be that same bus.\n\n\n\nMost mixers and DAWs automatically bus everything to the mix bus, which goes to the output of the mixer or DAW. However, we can use buses to route signals elsewhere in the mixer, like to subgroups and auxiliary tracks, before routing those channels ultimately to the mix bus.\n\n\n\nMixers with more buses have more routing capabilities than those with fewer.\n\n\n\nBuses are not audio tracks or MIDI tracks that contain audio clips or MIDI information. Rather they route audio within the mixer, console or DAW.\n\n\n\nIn analog devices, a bus refers to a physical point where multiple signals are summed together. In digital devices, this is done virtually through digital means.\n\n\n\nBusses are general-purpose and are, therefore, often vague in their description.\n\n\n\nMuch confusion about buses comes from how we discuss them in practice. For example, we'll often call our subgroups by their name followed by the word bus, i.e., drum bus, guitar bus, vocal bus, etc. When doing so, we often reference the subgroup channel on the mixer or DAW rather than the audio conduit that carries the audio signals themselves.\n\n\n\nSo if we want to be technically correct, it's better to call these "buses" subgroups.\n\n\n\nFor more info on using bussing in your mixes, check out my video below:\n\n\n\n\nhttps:\/\/youtu.be\/1CF6H2QC02c\n\n\n\n\nTo learn more about buses, check out my article What Are Audio Buses? (Mixing, Recording, Live Sound).\n\n\n\n\n\n\n\nWhat Is A Subgroup?\n\n\n\nSubgroups are groups of [typically] similar tracks\/channels summed together. These tracks are bussed together on the same bus, and the subgroup is the channel with that bus as the input.\n\n\n\nSubgroups are not audio tracks, meaning we can't record audio to them. Rather, they're set up to receive the outputs of other tracks in the mix via a common bus.\n\n\n\nSubgroups are sometimes referred to, often confusingly, as groups, bus groups, submixes, submasters, or even as "buses", depending on the gear or software.\n\n\n\nSubgroups are fantastic for simplifying a mix, especially when we're dealing with limited resources (outboard gear and\/or CPU). We can streamline the mixing process by having a dedicated channel and fader for a group of tracks.\n\n\n\nThere's a philosophy known as top-down mixing that starts processing the mix bus before moving onto the subgroups and finally to the individual track (if any more processing is even warranted by then).\n\n\n\nI have a video on top-down mixing worth checking out if you're interested in learning more:\n\n\n\n\nhttps:\/\/youtu.be\/8dMzxjsbeIU\n\n\n\n\nAs an aside, submixes can be defined slightly differently than subgroups. While subgroups are generally designed into the mixer itself, submixes generally utilize another, smaller mixer to mix a group of tracks into a composite signal (mono or stereo) and send that signal to the main mixer. The difference is subtle, and in modern DAWs and digital mixers, the two terms are often interchangeable.\n\n\n\nNot only can we process all the similar tracks together in the subgroup channel, but we can simplify our auxiliary sends by sending from the subgroup rather than from each track.\n\n\n\nSo if we need specific control over individual tracks, we can do so at the track level. However, it's much more convenient to work with subgroups in most cases!\n\n\n\nFor more information on subgroups, check out my article What Are Subgroups? (Audio Mixing, Recording, Live Sound).\n\n\n\n\n\n\n\nWhat Are Auxiliary Tracks, Sends And Returns?\n\n\n\nAn auxiliary channel or "aux track" is designed as a flexible routing option\/bus destination to take "sends" or outputs from the individual tracks and subgroups of the mixer.\n\n\n\nThe subgroup is one use of an auxiliary track. Another common use is the "aux send".\n\n\n\nAuxiliary tracks are not audio tracks (they do not record audio) but rather take in audio from other tracks within the mixer. When not used for subgroups, aux tracks will not be fed by the outputs of the tracks\/subgroups. Instead, each track\/channel will have some number of "sends" to effectively feed the channel's audio to the specified auxiliary track without affecting its output.\n\n\n\nAs a matter of semantics, some would argue that auxiliary tracks are different than subgroups. A subgroup is effectively set up on an "auxiliary track", though not all auxiliary tracks are set up as subgroups.\n\n\n\nWith the flexibility of modern digital audio workstations, the terms and definitions often overlap. In analog hardware mixers, which are much more limited, these distinctions hold more weight.\n\n\n\nFor example, a mixer could have four auxiliary sends. These sends are effectively buses that can combine signals from any of the tracks. Each send will route the signal from the track to its appropriate auxiliary channel. We can then do as we wish with each of the four auxiliary channels, all without affecting the output of the channels themselves (which can be routed to subgroups or straight to the mix bus).\n\n\n\nAuxiliary tracks are the aux tracks\/channels, complete with their own fader, inserts, sends, etc. They are incredibly flexible in their usage and are an important part of any mixer.\n\n\n\nLet's break down aux sends versus aux returns.\n\n\n\nThe aux send is the bus that allows us to mix varying levels of each channel and send them to the auxiliary track. These sends are typically potentiometers (real or virtual) so that we can send different amounts of each channel (or nothing from any channel) to the aux track in question.\n\n\n\nThese sends can often be configured to send the signal pre- or post-fader. Pre-fader means that the send pot will be the only control over the signal level sent to the aux track (at unity, it will send whatever signal level is in the channel\u2014generally after any internal processing\/inserts). Post-fader means that the fader position of the track will also affect the send level, along with the send pot position.\n\n\n\nFor more information on inserts, check out my article Audio: What Are Inserts? (Mixing, Recording & More).\n\n\n\nThe aux return is an auxiliary track that is outputted back into the mix (it's "returned" to the mix), often directly to the mix bus. These returns are used for many applications and are super flexible.\n\n\n\nLet's consider a few ways auxiliary tracks are used in mixing.\n\n\n\nAuxiliary tracks are often used for sending different mixes to foldback or in-ear monitors so that different musicians can have more or less of certain tracks in their monitor feed. We can effectively have different mixes by dialling in the send pots rather than the faders (which ultimately send to the mix bus).\n\n\n\nNote that when we're creating auxiliary mixes like this, the outputs of the auxiliary channels need to be separate from the main outputs. We output from the mixer\/console or the audio interface connected to our computer\/DAW to send the aux mixes where they need to go.\n\n\n\nWhen it comes to mixing the main mix, we can use auxiliary return channels for return effects and parallel processing.\n\n\n\nMultiple tracks or subgroups can be sent to the same aux return, and that aux track can be processed independently of the original channels. Remember that each channel will have its own send control to adjust the level being sent to the aux bus.\n\n\n\nEffects return channels, as they're often called, are popular for time-based effects like reverb and delay. Sending individual channels to a dedicated reverb or delay effects return channels gives us tremendous control over the space in the mix.\n\n\n\nI discuss how to use effects sends\/returns and the benefits of doing so in the following YouTube video:\n\n\n\n\nhttps:\/\/youtu.be\/fbtFjs8osDQ\n\n\n\n\nWe can glue tracks together with common time-based processing without having to insert these effects on each channel. We also have independent fader control over the time-based effect, meaning we can mix it perfectly, independent of the original tracks, and automate it to our liking.\n\n\n\nIt also means we can process the effects return (with EQ, compression, saturation, etc.) to help the time-based effect sit perfectly in the mix. These are controls that are extremely difficult to achieve when inserting effects directly on audio tracks.\n\n\n\nI talk about the concept of glue in more detail in this video.\n\n\n\nEffects return channels are also used for parallel processing, which is effectively the same as setting up independent time-based effects, routing-wise.\n\n\n\nParallel processing means that the aux bus output is routed to the mix bus as well, allowing the channels being sent to the aux bus to also be outputted to the same mix bus. This way, we are able to mix the processed audio from the aux with the tracks that feed the aux. In other words, we can process and mix the signals in parallel.\n\n\n\nCommon parallel processing techniques include parallel compression, saturation and aural exciting. In the same way that we set up the time-based effects sends, we can send multiple tracks or subgroups to an independent channel and process that channel with compression, saturation, saturation\/high-pass filter, or whatever else will enhance the mix.\n\n\n\nWhen mixing in parallel, we maintain our "dry" original channels and mix in completely "wet" processed channels (the aux returns). We can be aggressive with the parallel processing to add weight, colour and interest to the original tracks.\n\n\n\nWe can also insert multiple processes, including EQ, into the parallel channels to have them fit perfectly in the mix.\n\n\n\nI have a video dedicated to parallel processing. Check it out here:\n\n\n\n\nhttps:\/\/youtu.be\/JBvNdsTXImA\n\n\n\n\nI also have more specified videos on parallel compression and parallel saturation if you're interested.\n\n\n\nTo learn more about auxiliary tracks, check out my article Mixing\/Recording: What Are Auxiliary Tracks, Sends & Returns?\n\n\n\nLet's now move on to VCAs.\n\n\n\n\n\n\n\nWhat Is A VCA?\n\n\n\nVCA stands for voltage-controlled amplifier, an electronic amplifier that varies its gain depending on a control voltage.\n\n\n\nIn mixing, a VCA or VCA group is an independent fader that we can use to control the signal levels of multiple channels simultaneously without altering the channels' faders and without having to route the channels to their own subgroup.\n\n\n\nVCAs do not pass any audio signals and do not give us any channel controls (inserts, panning, sends, etc.). They are a voltage-controlled source that controls the volume level of the channels in the VCA group.\n\n\n\nTherefore, the channels of the VCA group will still be routed to their respective outputs. Additionally, the relative balance between the channels in the VCA group will remain intact regardless of the VCA fader position.\n\n\n\nVCA groups are yet another way to simplify the mixing process. We can choose to automate the VCA for even more control over the mix.\n\n\n\nVCA groups will have a fader and will sometimes offer mute and solo options, depending on the mixer\/DAW.\n\n\n\n\n\n\n\nWhat About Groups?\n\n\n\nAs we've already established, things can get a bit confusing in terms of semantics. The term "group" could be synonymous with "subgroup". However, in modern digital audio workstations, it generally means something different.\n\n\n\nIn terms of signal flow, modern DAW\/digital mixer groups do not have anything to do with routing. Rather, they link specific parameters and controls between the tracks\/subgroups of the group.\n\n\n\nFor example, if we have several tracks grouped together, we can set a multitude of options so that altering one track will produce the same relative results in the other track. Linked control options include:\n\n\n\n\nEditing: cuts, crossfades, nudges\/moves, clip gain adjustments, etc., made on one grouped audio track will be made on all other grouped audio tracks.\n\n\n\nInput: changing the input of one track will change the inputs of all other grouped tracks to match.\n\n\n\nRecord arm: arming one grouped track to record will arm all other grouped tracks to record.\n\n\n\nInserts: inserting a processor on one grouped track will insert that same processor in the same insert slot on all other grouped tracks.\n\n\n\nAuxiliary send: setting up an aux send on one grouped track will set up that same send on all other grouped tracks.\n\n\n\nSend levels: adjusting the send level on one grouped track will cause relative adjustments on all other grouped tracks.\n\n\n\nPanning: adjusting the pan position on one grouped track will cause a relative pan position adjustment on all other grouped tracks.\n\n\n\nFader position: adjusting the fader position on one grouped track will cause a relative fader repositioning on all other grouped tracks.\n\n\n\nOutput: changing the output of one grouped track will change the output of all other grouped tracks to match.\n\n\n\nSolo: soloing one grouped track will solo all other grouped tracks automatically.\n\n\n\nMute: muting one grouped track will mute all other grouped tracks automatically.\n\n\n\n\nChanging one parameter of one channel in a group changes that parameter in all channels of the group (whatever parameters you choose to link). Groups are great for editing and getting bulk mixing moves done quickly.\n\n\n\nFor more information on DAW groups, check out my article Audio: What Are Groups? (Mixing & Editing In DAWs).