If you connect the gate output to the trigger input of plaits the internal LPG will be strike and an external ADSR will not be necessary. Work fine for short percussive sounds. For other sounds shapes you will need an external module.
From the manual:
Trigger input. Serves four percussive purposes:
Triggers the internal decaying envelope generator.
Excites the physical and percussive models.
Strikes the internal low-pass gate (unless the LEVEL CV input [4] is patched).
Samples and holds the value of the MODEL CV input.
Adjusting the internal LPG and envelope
Hold the first button (A) and:
Turn the TIMBRE knob to adjust the response of the LPG, from VCFA to VCA.
Turn the MORPH knob to adjust the ringing time of the LPG and the decay time of the internal envelope.