Apple Logic Pro 9 - Manual (Page 1169)

To set a channel strip’s output format to surround
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Click-hold the Output slot of the channel strip, and choose Surround from the pop-up
menu.
The Pan control of the channel strip is replaced by a two-dimensional surround control.
The loudspeakers are represented by colored dots and the pan position is indicated by
a white dot that can be grabbed and moved.
To set the output format of multiple channel strips to surround
1 Select all channel strips that you want to set to surround output.
2 Click the Output slot of one of the selected channel strips, then choose Surround from
the pop-up menu.
Automatically Setting the Output Format of Channel Strips
Logic Pro automatically sets the output format of specific channel strip types, based on
a set of rules for each.
Audio Channel Strips
The channel strip of an empty audio track is automatically set to the format of the first
audio file added to it.
1169 Chapter 39 Working with Surround