This noise gate is a more aggressive expander, with an expansion ratio of 4:1. That means when the guitar has decayed to half its level below the treshold, it will be attenuated even more, resulting in one eighth of the original level. It is triggered later than the 2:1 gate, and with a more aggressive effect.
-Kemper Reference Manual
- Threshold - Sets the minimal volume level necessary to trigger the expander.
This is very useful for hardcore metal, where you are using quick mutes between aggressive riffing or chords.