Apple Logic Pro 9 - Manual (Page 287)

Side Chaining Plug-ins
All plug-ins that support side chain inputs feature an additional Side Chain menu at the
right of the plug-in window header. This allows you to route any audio, input, or aux
channel strip into the plug-in, via a side chain.
To route an instrument channel strip as the side chain signal (alternative approach)
1 Click the instrument channel strip’s Send slot, and choose an unused Bus from the pop-up
menu.
This creates an aux channel strip.
2 Click the Output slot of the aux channel strip, and choose No Output from the pop-up
menu.
This turns off the output signal of the aux channel strip, which you don’t want to hear.
3 Open the required plug-in from the instrument channel strip, and choose the
newly-created aux channel strip from the plug-in’s Side Chain menu.
The plug-in processes the audio of the aux channel strip selected in the Side Chain menu,
and not the audio of the instrument channel strip that the plug-in is inserted into.
The signal peaks of the side chain input (the sent instrument signal), combined with the
Threshold parameter of the plug-in, determine when the plug-in is triggered.
The following are some side chaining examples:
• A sustained pad sound is sent through a noise gate, which is triggered by a drum track
being used as the side chain input signal. This results in a rhythmic pad sound which
follows the signal peaks of the drum track.
• A noise gate inserted into a bass guitar channel is triggered by the kick drum track via
the side chain. This can tighten the timing of the bass guitar, as it follows the kick drum
signal.
• Side chains can also be used to blend a music mix with a voiceover. To achieve this,
the mix needs to be routed through a compressor which, in turn, is side chained, using
the voice-over track. In this type of setup, the music becomes softer when the narrator
is speaking, and louder when not. The effect is also known as ducking. Note that in
order for this to function, the Automatic Gain Make-up or Auto Gain control (if applicable
to the Compressor plug-in) must be disabled.
287 Chapter 10 Working with Instruments and Effects