Working with Multi-Channel Effects

Effects that are not available as true surround effects can be inserted as multi-channel effects on surround channels:  Logic Pro matches the surround format of a channel by automatically providing the required number of stereo and mono instances of the plug-in.

Learning About the Advanced Plug-in Header

Multi-channel effect plug-ins offer an advanced plug-in header.

Figure. Advanced plug-in header on multi-channel effect plug-in.

It can include a tab for each effect instance, an LFE tab, and a Configuration tab. The effect tab labels indicate if effect instances are loaded in stereo or mono. Channels joined with a “-” are loaded as a stereo instance. Channels separated with a “|” are mono. To explain:

  • L-R|Ls-Rs|C denotes left/right stereo, left/right surround stereo, and mono center.

  • L-R|Rs|C (a separate left surround tab is shown) denotes left/right stereo, mono right surround, mono center.

  • LR, C, and Ls-Rs shown on three separate tabs denotes left/right stereo, center mono, left/right surround in stereo.

Each effect tab is, in essence, a discrete effect unit for each channel (or channel pair). As such, you can have different plug-in parameters for the LR tab, the C tab, the Ls-Rs tab, and the LFE tab. When you save plug-in settings, the parameter values of each tab are saved.

You can assign these different mono or stereo configurations in the Configuration tab.

Configuring Multi-Channel Effects

The Configuration tab allows you to determine how parameter changes affect the plug-in instances.

Figure. Configuration tab.
  • Link menu: Determines which effects are linked. If you link effects, parameter changes apply to all effects in the linked group. You can choose between three groups:  A, B, and C. Channels set to none (“-”) operate independently. Each group features its own tab.
  • Bypass button: Click to bypass the channel:  It is routed around the effect. This is useful when individual channels should be exempt from processing by a particular plug-in.

Note: If the Bypass button of a grouped channel is clicked, all channels in the group are routed around the effect.

When a multi-channel plug-in is first inserted into a surround channel, it is automatically preconfigured to match the channel’s surround format, and to make the best use of the plug-in’s capabilities. For example, a plug-in with mono and stereo capabilities is inserted into a 5.1 bus. It is preconfigured as two stereo pairs, with the addition of a mono center and mono LFE channel. The necessary links and tabs are created automatically.

When you link channels, keep the following in mind:

  • If you link two channels as a stereo pair, the left channel is always assigned as the master.

  • If one or more channels are added to an existing group, the new members adopt the values of the group.

  • If you assign several channels to an unused group, the setting of the (front) Left channel is used for all group members.

Working with Side Chains

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.