Re: tc electronics Sentry Noise gate
If you google "TC Sentry manual", its literally the first result that pops up.
The Damp knob controls how much of the output signal is being gated (or, as they call it in the manual, attenuated) once the input signal from the guitar falls below the preset threshold. Basically, you stop playing, and the gate starts working, and the knob setting determins how much signal is still allowed to pass through.
The Decay knob controls how quickly the gate shuts. Higher settings wouldd be the equivalent of your angry dad pulling the plug on your amplifier to tell you to clean your damn room. Lower settings is your mommy dearest slowly turning down the volume knob in a nice, even fade, kindly informing you that it's high time to put the guitar away and clean your damn room.
From the user's manual: The three Sentry Noise Gate knobs control the “When?”, “How much?” and “How quickly?” of noise elimination.