XVIVE U4 In-Ear Monitor Wireless SystemThe Xvive U4 system is comprised of a transmitter unit, which connects to your audio source (typically a mixer or sound interface); and a belt pack receiver, to which you connect your earphones or headphones. Backup transmitter for U4 system Audiophile 24 bit 48 kHz sound with less than 5 ms of latency Industry standard 2. 4 GHz wireless technology Reliable, solid RF connection over a range of 90 feet