ToneMatch Mixer / De-esser
The De-esser removes some of the sibilance (S) sounds from the channel where you use it.
Threshold: 0 to -50 dB
As you lower the threshold, you increase the sensitivity of the De-esser.
At -50 dB it is more sensitive than 0 dB. At 0 dB it may not appear to be doing at all unless the (S) sounds are really pronounced.
Gain: 0 to 30 dB
When the De-esser removes sound (because the sound is greater than the Threshold), the overall sound may drop in volume. The Gain control turns the volume back up to compensate. At 0 dB you won't hear any difference.