Quick guide to Busses and Auxes

Here's a rundown about how busses and auxes work in Logic and a few of their finer points of operation.

Just to sort out one thing right off the top: a bus (line) is different than a bus object. The bus line is invisible but the bus object has a fader attached to it and looks much like the channel strip for an audio track except that it has no sends.

This is good to know because you can have a situation where you are sending from a track through the bus line to an aux object with a reverb inserted on it but when you mute the aux object you are still hearing the dry send signal coming out the main output. That's because there's a bus object with the same number as the bus line living in your environment and it's output is set to "output 1-2". You will have to change the output of the bus object to "no output" so that the signal only comes out the aux.

A bus (line) is always stereo. It's a pipeline from one object to another, usually from an audio or instrument track to a bus object or aux object. You can send or route both stereo and mono signals down the bus but the bus line itself is always stereo.

On the other hand, bus objects and aux objects can be either mono or stereo. Click on the circle/double circle at the bottom of the channel strip to change the mono/stereo setting.

A bus object will always recieve from the same numbered bus line (bus object 6 recieves from bus line 6) whereas an aux object can recieve from any bus line. So you could use the same bus line to output at multiple auxes.

A bus Object is inserted on the bus itself, before any Aux Object can access it. It alters the signal on the Bus, if you have any inserts on the bus channel.

An Aux Object "taps" the signal from a Bus, but doesn't alter the signal on the Bus.

Two ways to use a bus line: send to it from the track sends or you can change the output of the track to route the whole track down the bus line. The first situation would be for something like reverb, the second for something like outputting all your BG vocals to one Aux.

If you send/route a stereo signal down the bus line that's what comes out the other end, assuming you have a stereo bus object or aux object at the end.

If you send/route a mono signal down the bus line, ditto, as above.

Bus objects don't have sends, aux objects have sends. So you could use an aux with reverb inserted on it and send some of that reverb to another aux with a delay inserted there.

You can't pan a send down the bus line UNLESS you insert a Direction Mixer on a track.

The DM will work on stereo or mono tracks. It will also pan the whole track, not just the signal to the sends.

If you are routing a whole track down a bus line, (the track's output gets changed to a bus line) then the panning of the track will be preserved in the stereo bus line. Great for panned BGs, stereo guitars, drum mixes, etc

And finally, to use any of these options, go to the Send, I/O and Output buttons on your channel strip where you'll find a variety of menus where you can select busses, outputs and so on.

PS - Under "wish list" is the ability to have a bus output directly to an audio track. Much requested feature but as of yet not implemented in Logic.

[edit from admin:]You can vote for that feature here: http://www.logicprohelp.com/newfeatures.php