The DU30b is a microphone preamp and background music preamp. When an announcement is made into the microphone, the music is automatically "ducked" under the announcement. Then the music is brought back to it′s previous level.
 
Specifications
Input Impedance: 100K Ohms unbalanced, 600 Ohms balanced
Frequency Response: 20 Hz - 40 kHz
THD + Noise: < 0.03% typical
Noise Floor: -78 dB
Indicators: Power LED
Input/Output jacks: XLR balanced Input, RCA unbalanced input and output
Size: 4" x 4" x 1.5"
Weight: 1 lb. (.5 kg)
Power: 12 - 16 VDC 50mA, 5 x 1.2 mm DC Jack - Center Negative
Automatically ducks music under announcements
Perfect for restaurants and small clubs
* Clean, Quiet Mic Preamp