Dynamics processors typically use the detected amplitude of their input signal to trigger gain reduction. This split-off signal is known as the side-chain. Compressor/Limiter and Expander/Gate processing features external key capabilities and filters for the side-chain.
With external key side-chain processing, you trigger dynamics processing using an external signal (such as a separate reference track or audio source) instead of the input signal. This external source is known as the key input.
With side-chain filters, you can make dynamics processing more or less sensitive to certain frequencies. For example, you might configure the side-chain so that certain lower frequencies on a drum track trigger dynamics processing.
The Source selector lets you set the source for side chain processing: Internal, Key, or All-Linked.
If Internal is selected, the plug-in uses the amplitude of the input signal to trigger dynamics processing. With greater-than-stereo multichannel processing, the input signal for each stereo pair effects only those same channels, and likewise mono channels are effected only by their own input signal. For example, with an LCR multichannel format, the processing for the Center channel is only triggered when the Center channel input signal reaches the threshold. However, when the input signal reaches the threshold on the Left or the Right channel, processing is triggered for both the Left and the Right channel.
If Key is selected, the plug-in uses the amplitude of a separate reference track or external audio source to trigger dynamics processing. The reference track used is selected using the Plug-In Key Input selector in the Plug-In window header. With greater-than-stereo multichannel processing, the key signal triggers dynamics processing for all processed audio channels equally.
If All-Linked is selected, dynamics processing is applied equally to all channels when the input signal reaches the threshold on any input channel, except for the LFE channel (if present). The LFE channel is processed independently based on its own input signal.
Select the Peak option to apply side-chain processing according to the detected peak amplitude.
Select the Average option to apply side-chain processing according to the detected average amplitude.
Four Filter Type options are available for side-chain processing:
Select the Low Pass option to apply a low pass filter to the side-chain processing at the selected frequency.
Select the High Pass option to apply a high pass filter to the side-chain processing at the selected frequency.
Select the Notch option to apply a notch filter to the side-chain processing at the selected frequency.
Select the Band Pass option to apply a band pass filter to the side-chain processing at the selected frequency.
The Side Chain Processing Graph display shows the frequency curve for the selected Filter Type at the selected Filter Frequency.