The Dcode TB-1 is a battery operated talk-back system for microphone boom operators. The TB-1 enables the mixer and two boom locations to maintain full duplex telephone style communications.Also features a call light to signal all operators in the system.Features:Full duplex talk-back between all stations.Internal microphone for when an external mic is not needed.Call light for signaling any station when momentary talk is pressed.Left & Right Program Input to mix left and right making the TB-1 a stand alone monitor system.Three level volume switch using standard stereo headphones.Quick change battery compartment.Low voltage indicator alerts user when battery running low.Specifications:Size: 3.25" x 4.6" x 1.25"Weight: 11 oz Power: One 9 volt alkaline battery per box. Low battery indicator lights at 5 voths. Impedance = 100k OHM/input.Drives standard 70 OHM stereo headphones.Approximately 70 db dynamic range.Operates on a single pair using standard XLR 3 pin microphone cables.