Multi-mono effects in Logic Pro for Mac
The plug-in window of a native plug-in (mono, stereo, or surround) has a single effects pane displaying the parameters and controls that affect all channels of that plug-in equally.
Any effect plug-in that is not available in a native surround format (for example, 5.1 or 7.1.4) can be inserted in a surround channel strip in multi-mono mode. In that case, Logic Pro loads that plug-in multiple times, referred to as multiple instances. Each instance represents a mono or stereo channel to match the project surround format by automatically providing the required number of stereo and mono instances of the plug-in. When you click the plug-in button on a channel strip, it still opens only a single plug-in window, but with additional functionality for those multiple instances.
With a plug-in inserted in multi-mono mode, you can adjust the effect parameters for each plug-in instance separately or as groups. For example, with the Channel EQ plug-in, you can roll off the frequency for the LFE channel while applying a high-frequency boost for the center channel without affecting any other channel.
Plug-ins loaded in multi-mono mode have an extended plug-in header that contains the various channel buttons, the Couple button, and the Configuration button 
, which switches the plug-in window to a different pane for creating those groups. For more information, see Configure multi-mono effects.
The labels on the channel buttons indicate whether effect instances are loaded in stereo or mono. Channels joined with a hyphen (-) are loaded as a stereo instance, and channels separated with a vertical bar (|) are mono.
L-R|Ls-Rs|C: Denotes left/right stereo, left/right surround stereo, mono center.
L-R|Rs|C (a separate left surround button is shown): Denotes left/right stereo, mono right surround, mono center.
L-R, C, and Ls-Rs shown on three separate buttons: Denotes left/right stereo, center mono, left/right surround in stereo.
Couple button: When active, this applies the parameter changes you make in one pane to the same parameters in the other panes.
Each effect pane addresses a discrete effect unit for each channel or group of channels. Each button can have different parameter settings.
Click each channel button to change the pane displaying the settings of the plug-in parameters for that specific channel or group of channels. The parameter values of each pane are memorized when you save a plug-in setting.
Side chains and surround effects
When inserting a side chain–capable plug-in, the side chain source (selected in the plug-in header) is routed to all surround instances.
The detection circuits of grouped plug-in instances are linked, and react as one unit. This ensures that the spatial surround image is not skewed or deformed.
Note: This is also true when no side chain input is selected. In this case, the group’s combined individual inputs are used to feed the linked detection circuit—effectively acting like a side chain source.