A microphone splitter is a device with an input from a microphone and multiple outputs. It is also known as a "rathouse" due to the large amount of cabling involved. A splitter is often used at larger venues to provide feeds from microphones or other sources to both a front of house mixing desk and a monitor desk. This allows the monitor mix to be different from the house mix, so that the musicians may hear a mix with certain instruments emphasized, which can assist in achieving a feeling of "tightness".
In a simple splitter the outputs are connected in parallel, with no isolation between outputs. In cases where each output is connected to a system with a different ground potential, this can cause ground loops, a common source of noise in an audio system. To provide isolation and prevent ground loops, outputs may be connected via a splitting transformer or a number of buffer amplifiers.
Each additional output puts additional load on the source, which can cause signal degradation. Active splitters with buffer amplifiers (also known as a distribution amplifier) are the only solution to provide an unlimited number of splits, but are costly.