The MX5.1 Mixer is a SURROUND mono input line mixer with many features of a large frame console. The MX5.1 has a unique MUTE circuit that when pressed, the LED turns RED, but when the module is ON, the LED serves as a level presence indicator, illuminating green to show signal presence. There is a PB board selector jumper to choose between PRE (factory standard) and POST for the level led. This is very useful in live recording when you need to know quickly if a channel has signal or which has the loudest signal on it. It is also perfect for identifying which channel has the Kick and which has the Snare, etc.