The envelope is used to shape the filter cutoff over time. When the input signal exceeds the set threshold level, the envelope is triggered.

Envelope parameters
Attack knob and field: Set the attack time for the envelope.
Decay knob and field: Set the decay time for the envelope.
Sustain knob and field: Set the sustain time for the envelope. If the input signal falls below the threshold level before the envelope sustain phase, the release phase is triggered.
Release knob and field: Set the release time for the envelope. This is triggered as soon as the input signal falls below the threshold.
Dynamic knob and field: Determine the input signal modulation amount. You can modulate the peak value of the envelope section by varying this control.
Cutoff Mod. slider and field: Determine the impact of the envelope on the cutoff frequency.