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Busses

Postby JRocker » Thu Nov 14, 2019 12:09 pm

Pardon my ignorance, but I read a lot about 'bus' this and 'sub bus' that...and have no idea what it's all about or actually what it means! I assume this is something to do with the mixing process and not really during the recording process? Is there any 'bus for beginners' type article I can read that can help me understand and how it work?
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Re: Busses

Postby jimjazzdad » Thu Nov 14, 2019 12:32 pm

Others more erudite than me will likely have answers for you shortly, but a simple analogy has helped me to understand buses. A bus in a mixer is like a highway (or carriageway for some of you); it carries signal from an on-ramp - inputs, input preamps, etc. - to a destination - an output of some kind. Depending on where you want the signal to go, you can choose different buses (highways) to get to different outputs (destinations). The main stereo mix bus will direct signals to the main left and right outputs, control room monitor outputs, etc. Auxiliary buses might take signals to effects processors, monitoring chains, etc. In an analogue mixer buses are physical wires or copper traces on a PCB; in digital mixers or your DAW they are virtual buses that are determined by the combination of software and hardware. Clear as mud now?
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Re: Busses

Postby JRocker » Thu Nov 14, 2019 12:38 pm

>Clear as mud now?<

No, more confused as ever now!
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Re: Busses

Postby Wonks » Thu Nov 14, 2019 12:39 pm

A bus in physical mixer term, is a wire or track that links the output from a number of channels together and connects them to another section.

The main stereo bus is the primary output bus that connects the output of the input channels to the input of the master output section. An auxiliary bus is the connection that links the outputs of channels' aux outputs (e.g. all the aux 1 send controls) to the aux master send control (e.g. aux 1 master level).

More complex hardware mixers have additional sub-buses that you can assign a mixer channel to instead of the main stereo bus. These work in pairs, just like the main stereo bus, and have dedicated faders for the sub-channels, which then feed into the main stereo bus.

This allows you to assign say all the drum mics to a pair of sub-buses, so that you can create the relative mix on the channel output faders, but control the overall level of the drums on a pair of faders, allowing for easy overall volume adjustment - rather than having to move say 8 different channel faders at the same time.

In a DAW, the hardwired connections are obviously replaced by software connections, and the freely configurable nature of most DAWs allows you to create all number of sub-buses and sub-sub buses that a hardware mixer couldn't.

The term 'master bus' is really a misnomer, as it normally refers not to the bus itself, but to the master output section. On a hardware mixer, there would be insert points on this where you can connect hardware processors. DAWs give you numerous slots to input plug-ins to compress, limit and EQ the overall stereo sound. It's this processing that's what's generally meant when talking about "master bus processing', rather than the bus itself and the master output faders.
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Re: Busses

Postby Arpangel » Thu Nov 14, 2019 12:49 pm

Sorry Wonks, you got there before me!

A bus is like a real Bus! It takes a collection of signals (people!) or tracks, to a single/multiple destination.
On a mixer or a DAW you'd have your inputs, or recording tracks, and a mixer would have routing buttons, so you could send say 6 mixer channels to sub group faders 1/2 so that instead of having to ride six faders, you now have your drum mix on two faders.
In a DAW it works more or less the same, except the methods of 'grouping" tracks into busses varies. The word bus has a lot of uses in recording, but just remember it's a collection of tracks or signals that are being collectively routed to another condensed destination. These "sub-mixes" can then be routed to the main "mix bus" and further reduced in terms of tracks and channels, down to a stereo mix.
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Re: Busses

Postby CS70 » Thu Nov 14, 2019 1:34 pm

JRocker wrote:Pardon my ignorance, but I read a lot about 'bus' this and 'sub bus' that...and have no idea what it's all about or actually what it means! I assume this is something to do with the mixing process and not really during the recording process? Is there any 'bus for beginners' type article I can read that can help me understand and how it work?

A bus is a channel which receives its signal from other channels. You can recognize it because it doesn't have any external input (like a preamp or other input).

The most common bus is the "main" or "master" bus. All channels send to it implicitly, but it doesn't have any input to which you can connect, say, a microphone.

A bus is called "bus" because - unlike a channel - you can send to it as many signals as you like and they get all added to it (aka "mixed").

For the master bus, by definition, all the regular channel send to it and the bus output is the mix.

In theory you don't need any other bus.

But in practice having several of them makes things much easier - because it allows you to group several signals and treat them as a whole (for example, applying EQ and effects) and have one single fader to control the result level.

So say for example you have a drum kit, with 8 microphones for kick, snare, toms and overheads. Each mic is connected to a separate channel (via the channel preamp, usually). You can of course set the individual levels of the channel and EQ and treat with effects. After a while, you have the faders in different positions to achieve your perfect balance between snare, kick, toms and overheads.

But say you want to be able to quickly change the overall level of the entire kit. You have to move 8 faders. The faders are logarithmic, so if they're not in the same position, the actual change you make by moving them the same linear amount results in different level changes. In other words, it's a mess - you risk all the time to change your precious balance.

But if you send the result to a "drums" bus instead of the "master", and set the drums bus to send to the master (which is the default), the problem is solved: by moving the fader of the drum bus you can change its total level in one go.

Suddenly you have separate control for your internal kit balance (the channel faders) and the kit as a whole, so you can change one without affecting the others.

And since buses are most often like regular channels (only without an external input stage), you can apply EQ, add effects, mute them, solo them etc.

Physical desks have limited space and therefore a limited amount of buses - meaning you can "group" channels only so far.

DAWs have infinite buses, which makes it much simpler to create complex mixes without losing control.

Typical buses are space reverbs (all signals get sent to them and a little bit of the bus is fed to the master so that it adds the feel that all instruments are played in the same space), instrument subgroups (drum kit like above, but also rhythm guitars, multiple backing vocals etc) - basically every time you want to treat a group of signals as a whole.
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Re: Busses

Postby Hugh Robjohns » Thu Nov 14, 2019 1:45 pm

A 'bus' collects a number of different signals and mixes them together. It may be a real physical thing -- like a piece of wire running across the full width of a console under each input channel -- or it cold be a notional thing in the code of a virtual mixer in a DAW etc.

The name comes from a 'bus-bar' which is a length of metal strip used to connect things together in electrical power distribution systems.

In a physical mixer, buses can operate in a variety of different ways depending on the design. Some add signal voltages together. Some sum signal currents. Some feed into transformers and some into active electronic circuits of various types... but fundamentally they always combined multiple signals from any number of different sources to create a mixed composite. You can usually control which and how many separate signal sources are connected to each bus, and the level of each contributing signal.

So a simple mixer will have a stereo mix bus, which is actually two 'buses', one for the left channel and another for the right, to which all the channels contribute and get mixed together. Those combined signals may then be passed through a master fader, say, and on to the main stereo output.

In a larger mixer you might have sub-buses, so some channels might be combined first so they can be controlled separately as a group, and then that mixed group might be sent to the mains stereo mix bus to be combined with other channels...

Other buses will collect signals for the various auxiliary sends, tape recorder feeds, matrix outputs, and so on...

And finally, in the UK (and certainly in the SOS magazine) we tend to use 'bus' or 'buses' ... but our colleagues on the other side of the Atlantic generally use 'buss' or 'busses' ... but they are the same thing!

Technical terms like this are explained in our online Glossary:

https://www.soundonsound.com/sound-advice/glossary-technical-terms

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Re: Busses

Postby blinddrew » Thu Nov 14, 2019 5:15 pm

Hugh Robjohns wrote:And finally, in the UK (and certainly in the SOS magazine) we tend to use 'bus' or 'buses' ... but our colleagues on the other side of the Atlantic generally use 'buss' or 'busses' ... but they are the same thing!
This has been bugging me for years! :thumbup:
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Re: Busses

Postby Wonks » Thu Nov 14, 2019 5:57 pm

Or 'buggging you'. :D
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Re: Busses

Postby JRocker » Thu Nov 14, 2019 9:16 pm

Thank you to all who have replied with your helpful explanations. Finally, I have understood it all! Much appreciated to everyone who took the time to help me out. Thank you.
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Re: Busses

Postby Wonks » Thu Nov 14, 2019 10:39 pm

:thumbup:
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