Hey to all
,
I got it. I found this
here. For all people who want to know what it is just the explanation:
Loopback activated: If I record something, I record the sounds on my Computer AND the sounds of the instruments over Interface.
For example: If I open a mp3-Song in my Computer and to the same time am singing in a mic, which is connected over interface to my Computer, then I can record both together in one file or track.