Summary: A bus can be pre or post fader, and the gain can be set to specify how much signal comes from each input.
A bus is a special type of group that receives audio from an input track or tracks. The amount of signal coming from each input track is dependent upon its send level to that bus. Buses are useful when you want to have several tracks that use the same effects. Not only does this reduce CPU usage, but the parameters of the effects only have to be changed in one place instead of two. See Buses for more information.
There are several different ways to add a bus to a document. To add an empty bus, choose Add Bus… from the Edit menu. This will present the following sheet that allows you to specify the bus name, color, and number of channels:
This dialog is also used to edit an existing bus (to change the name, color, or number of channels).
To create a new bus and assign it to an existing input track, go to the send section of the input track you want to add a send too. Click on an empty send popup menu and select Create Bus…
A bus will be created for you and your input track will be added as a source to that bus. The send section expands to give you a send level control and an additional empty send slot will be added. As shown above in the right most image, the name of the newly created bus is visible in the topmost send popup.
You can create as many buses for a track as you need.
An input track can send its audio to any number of buses. The bus can be created at the time of the send assignment, or an assignment can be made to an existing bus.
The bus popup will always show the names of all existing buses that a track can send to. In the example to the left, we created a new bus by choosing Create Bus… and had two additional buses in our document. When we click on the popup menu of our unused second send, we see a list that contains Bus 1, Reverb Bus, and Post Effects. Note that the Bus 1 item is disabled because it has already been assigned to the bus. If we were to choose Reverb Bus, a new assignment would be made to the bus named Reverb Bus. Thus this input track would then send its audio to two buses, Bus 1 and Reverb Bus.
To change a bus assignment, select the new bus from the popup menu. A bus assignment can be removed by changing the bus to None. This does not delete the bus track from the document. It removes that send of the input track to its previously selected bus.
Send buses can be configured pre or post fader. To set this option, select Pre Fader or Post Fader from the send popup menu. Pre fader buses send audio before the volume mixing stage of the track, and post fader buses send audio after the volume mixing stage of the track.
You can specify how much of the audio signal is sent to the bus by changing the value of the control beneath the send popup menu. The initial send gain is 0 db or Unity gain. To increase the gain or amount of signal that is sent to the bus, drag the control bar to the right. To decrease the gain, drag the control bar to the left. You may also edit the value numerically by clicking in the gain value text box and typing the new value followed by a Return or Enter key.
To remove a send, choose None from the popup menu of the send you which to remove. This does not delete the bus track from the document. It removes the input track from the source of the Bus. To delete a bus from the document, select it and press Command-Delete or choose Remove Selected Group from the Edit menu.