Surround Compressor controls in Final Cut Pro for Mac
Surround Compressor provides the following controls.
To add the Surround Compressor effect to a clip and show the effect’s controls, see Add Logic effects to clips in Final Cut Pro for Mac.
Link controls

- Circuit Type pop-up menu: Choose the type of circuit emulated by the Surround Compressor. The choices are Platinum, Classic A_R, Classic A_U, VCA, FET, and Opto (optical). 
- Grp. (Group) pop-up menus: Set group membership for each channel—A, B, C, or no group (indicated by -). Moving the Threshold or Output Level slider for any grouped channel moves the sliders for all channels assigned to that group. - Tip: Press Option and Command while moving the Threshold or Output Level slider of a grouped channel to temporarily unlink the channel from the group. This allows you to make independent threshold settings while maintaining the side-chain detection link necessary for a stable surround image. 
- Byp (Bypass) buttons: Bypass the channel. If the channel belongs to a group, all channels in the group are bypassed. 
- Detection pop-up menu: Choose whether Surround Compressor uses the maximum level of each signal (Max) or the summed level of all signals (Sum) to exceed or fall below the threshold. - If Max is chosen, and any of the surround channels exceed or fall below the threshold, those channels (or grouped channels) are compressed. 
- If Sum is chosen, the combined level of all channels must exceed the threshold before compression occurs. 
 
Main controls

- Ratio knob and field: Set the ratio of signal reduction when the threshold is exceeded. 
- Knee knob and field: Determine the ratio of compression at levels close to the threshold. 
- Attack knob and field: Set the amount of time it takes to reach full compression, after the signal exceeds the threshold. 
- Release knob and field: Set the amount of time it takes to return to 0 compression, after the signal falls below the threshold. 
- Auto button: Make the release time dynamically adjust to the audio material. 
- Limiter button: Turn limiting for the main channels on or off. 
- Threshold knob and field: Set the threshold for the limiter on the main channels. 
- Main Compressor Thresholds sliders and fields: Set the threshold level for each channel—including the LFE channel, which also has independent controls. 
- Main Output Levels sliders and fields: Set the output level for each channel—including the LFE channel, which also has independent controls. 
LFE controls

- Ratio knob and field: Set the compression ratio for the LFE channel. 
- Knee knob and field: Set the knee for the LFE channel. 
- Attack knob and field: Set the attack time for the LFE channel. 
- Release knob and field: Set the release time for the LFE channel. 
- Auto button: Make the release time dynamically adjust to the audio material. 
- Threshold knob and field: Set the threshold for the limiter on the LFE channel. 
- Limiter button: Turn limiting on or off for the LFE channel. 
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