Impact provides side-chain processing capabilities. Compressors typically use the detected amplitude of their input signal to cause gain reduction. This split-off signal is called the side-chain. However, an external signal (referred to as the Key Input) can be used to trigger compression.
A typical use for side-chain processing is to control the dynamics of one audio signal using the dynamics of another signal (referred to as the Key Input). For example, you could use a lead vocal track to trigger compression of a background vocal track so that their dynamics match.
To use a Key Input signal for side-chain processing:
1 Click the Send button and select a bus path for the audio track or Auxiliary Input you want to use as the side-chain signal.
2 From Impact’s Key Input menu, select the input or bus path carrying the audio you want to use as the side-chain signal to trigger Impact compression. The Key Input source must be monophonic.
4 Begin playback. Impact uses the input or bus that you selected as a Key Input to trigger its effect.
5 If you want to hear the audio source you have selected as the side-chain input, click Listen. (To stop listening to the side-chain input, click Listen again).
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6 Adjust Impact’s Threshold parameter to fine-tune Key Input triggering.