Hi Jimmyboy,
Think of Gain as a magnifier. The higher you raise it, the more it magnifies target signals, making them appear larger.
The Threshold is split into two features:
From settings of -9 to 0, think of the threshold control as a door. The door is shut at -9 and the door is fully open at 0.
From settings of +1 to +9, think of the threshold control as a volume control that makes all the signals that got into the wide open door louder and easier to hear.
Thats kind of an over simplified description of the controls but pretty accurate nonetheless. The combination of the three features give the user a lot of control over the detector. Add the 4 different tone modes to it and the F5 has a lot going on with the audio.
When setting up the detector, think, "how big do I want the signal to be (GAIN) and, how large of a signal do I want coming through the door (THRESHOLD)" and if you have the door wide open (threshold at 0), then how loud do I want the tiniest signals (threshold above 0)
Then of course, the actual site conditions laugh at you and say, "sorry buddy, but you're going to have to make the signals smaller or close the door a little." And then the two of you work out the best compromise for the targets you are after
HH
Mike