audiodynamic: Threshold

Could someone explain how the threshold property works on the audiodynamic element (https://gstreamer.freedesktop.org/documentation/audiofx/audiodynamic.html?gi-language=c)? I was expecting it to be a value representing the decibel value but it's set to only be between 0-1 (using gst-inspect).

Is 0-1 meant to map a certain decibel range e.g. 0-1 : 0-60 or is it something more complicated and if so, could you provide an example if I wanted to set it to like -30dB.