The MB15 ProMatch converts consumer level stereo RCA signals to balanced XLR professional line level, and back. One side of the unit, labeled 1, has two XLR inputs and stereo RCA outputs. The other side labeled 2, has stereo RCA inputs and two XLR outputs. Each side has stereo level controls, and an LED indicates that power is applied to the unit. An additional benefit of the MB15 is that it will act as a balanced XLR line level control. By adding a stereo pair jumper between the four RCA jacks (connecting ins to outs), the two Level controls may be inserted into any balanced XLR line.