Apple Logic Pro 9 - Manual (Page 1174)

The separation square is visible if the extended parameter section is open. If the extended
parameter section is closed, it remains visible if any of the separation values does not
equal 1.00. It also stays visible when the default values are reached by editing the square
graphically. Closing the extended parameter section (with all separation values at 100%)
makes the square disappear.
You can Option-click the value field or sliders shown in the extended parameters (or on
the separation square lines) to reset them to default values.
Note: In 7.1 ITU surround formats, the Separation of Left Middle and Right Middle is
determined by the average separation value of the Front and Rear channels.
Using the Stereo-to-Surround Panner
If the source input is set to stereo, the Stereo-to-Surround Panner appears.
It is similar to the Mono-to-Surround Panner, but features three pan pucks: a puck for
the L(eft) signal, a puck for the R(ight) signal, and a third puck, which controls both the
L and R pucks as a group. It also offers a Spread field in the upper-right corner, which
controls the stereo width of the signal.
Moving the L or R puck in the surround field moves the second puck in a symmetrical
fashion. Dragging the third puck moves both the L and R pucks, while maintaining a
given spread.
A left/right movement changes the angle of both, an up/down movement changes the
diversity. The circular bars around the panner indicate which speakers will carry the
respective signal source; the closer to the center a puck is moved, the wider the
corresponding bar gets (the greater the diversity, in other words).
1174 Chapter 39 Working with Surround