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What is the 'bus' in a mixing console? Where does it go? What is the fare?

Buses are a feature of both analog and digital mixing consoles. You can't see them, you can't control them. So what are they, and what do they do?

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Think of an individual signal cable. It carries one signal from one output to one input. It isolates that signal from other nearby cables, and also protects the signal against interference.

So to take one signal from A to B, a cable is a great way to do it. It's like a taxi cab, taking one passenger from one place to another.

A bus however is more versatile. It can carry several signals to a single destination. It could have multiple destinations but generally there is only one.

This is ideal for a mixing console. As many signals as you want, from the channel strips, can be mixed onto a bus, then the output of that bus can be controlled in level by a single fader, generally known as the group fader (sometimes subgroup fader).

This is like a London bus bus picking up passengers from a variety of stops near their homes in suburbia, and taking them to the city center and dropping them all off.

A mixing console is often specified as 12/2 (twelve into two), or 32/8. The first figure is the number of channels, the second the number of group outputs into which those channels can be mixed.

So a 32/8 mixing console has at least eight buses.

In practice there will be more. If it also has four auxiliary sends, then there will be four aux buses. If it has a solo or PFL facility, it will have a solo/PFL bus.

All of the above refers to analog consoles. Digital consoles have buses too, conceptually, because they mimic the way analog consoles work. (Now there's a wheel that doesn't need reinventing!).

But digital mixing often uses buses more flexibly. For example in Pro Tools you can output a number of signals to a bus, then assign that bus to an auxiliary channel and apply overall EQ, reverb, and control the level of all of the signals on the bus.

There's no mystery to buses. Except why 'bus' is often spelt 'buss'. It doesn't matter - you can spell it either way.

[Note - Sometimes a console has a 'bus trim' control. This has exactly the same function as a group fader.]

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By David Mellor Saturday October 29, 2005
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