The MB15 ProMatch converts consumer level stereo RCA signals to balanced XLR professional line level, & back.
One side of the unit, labeled 1, has two XLR inputs & stereo RCA outputs.
The other side labeled 2, has stereo RCA inputs & two XLR outputs.
Each side has stereo level controls, & 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