Threshold Follower is an envelope generator with a threshold that is compared to
the incoming audio signal's amplitude. When the signal's amplitude exceeds the selected
threshold, the envelope's attack stage is triggered.
When the signal falls below the threshold the envelope enters the release stage.
The envelope's behaviour is linear.
This parameter sets the threshold on which the audio switches from attack or release.
audio input is louder than the threshold, the envelope will switch to attack stage
and rise. If it is
lower then the threshold, the envelope will switch to the release stage and fall.