Audio-volume /w input Sound.sampled

Hey guys, I'm quite new to Java and wanted to access the Volume of the Mic-Sound for a
simple Audio-Visualizer. I got everything working except for my AudioInput class.
It doesn't throw exceptions or errors but the line.getlevel returns constantly -1.
If anyone has experience with that and could tell me what is wrong, it would be awesome.

My AudioInput class:

Code (Java):

package audio;

import javax.sound.sampled.AudioFormat;
import javax.sound.sampled.AudioSystem;
import...

Audio-volume /w input Sound.sampled

Audio-volume /w input Sound.sampled