I found a way how to use Audacity and to listen real time.
If you don't see a mic volume control in the main mixer, in the Volume Control window, choose Options - Properties, click on Microphone to make a check mark appear - after the the Mic Volume will appear in the mixer settings.Unmute it and have fun.
I read there is program to video datalog screen, which could be good if Megatune and Audacity are started and listen for knock at the same time. Let's see if I can find it.