Some interfaces have external or built-in potentiometers for the audio input adjustment to the soundcard. Unfortunately, this potentiometer is adjusted in some interfaces for a minimum volume output and it is not appropiate for weak signals detection. Test have shown that you could loss until 10 dB of reception if this potentiometer is not properly adjusted.
Recommended to adjust this potentiometer for the maximum audio. After, adjust the audio input properly using the Windows Audio Mixer until the ROS VU marks about -5 dB or -4 dB.