PreSonus ACP22 - Manual (Page 11)

Controls & Connections
'CLOSE' LED above the threshold knob indicates when the gate is closed
(the signal level is below the threshold). If the threshold is set fully
counter-clockwise, the gate is turned off (always open), allowing all signals
to pass through unaffected.
Attack
The gate attack time setting determines the rate at which the gate opens.
Faster attack times are normally useful for gating percussive instruments
such as drums, etc. Slowing the attack time will eliminate any 'pops' are
'clicks' in the gate when gating vocals, instruments, etc.
Release
The gate release time determines the rate (speed) at which the gate
closes. This is indicated by observing the OPEN and CLOSE LED's. As the
release time is lengthened (clockwise), you will notice
that the CLOSE LED reflects the close time. Release times should typically
be set so that the natural decay of the instrument or vocal being gated is not
affected. Shorter release times help to clean up the noise in a signal but care
must be taken, especially with regards to percussive instruments, to avoid
gate 'chatter'. Longer release times usually eliminate 'chattering' and should
be set by listening carefully for the most natural release of the signal to
which the gate is being applied.
Range
The gate range button sets the amount of gain reduction occurring when
the gate closes. Therefore, if the range button is pushed in (led on), the signal
will be gated (reduced) by 60dB as it crosses below the threshold. If the gate
range button is out (led off), the signal will be gated (reduced) by 6dB as it
crosses below the threshold. The CLOSE LED above the threshold knob
indicates this by changing brightness relative to the range amount. When the
range is set to 60dB, the CLOSE LED will illuminate to its brightest level at
the end of the release time which has been set by way of the release control.
Filter
The filter feature of your ACP-22 modifies the audio signal such that
the gate is less sensitive to high frequency instruments. This means that when
the filter is active, the gate will only open for those instruments with lower
frequencies. The filter is set for -6dB at 2.5kHz. The filter rolls off the high