The SLX4 receiver brings unprecedented ease of use to wireless with Automatic Frequency Selection and Automatic Transmitter Setup. For use with SLX Wireless. With included rack hardware and detachable antennas, it is ready for immediate installation right out of the box. Model SLX4L is available with logic output for use with software echo cancellation and remote battery life monitoring. Logic-enabled transmitters include MX690 and MX890. SLX Wireless Systems feature Shure's patented Audio Reference Companding for crystal-clear sound beyond the limits of conventional wireless technology. SLX Wireless Systems feature Shure's patented Audio Reference Companding for crystal-clear sound beyond the limits of conventional wireless technology.