It supports the mute function when there is no signal for the receiver; You can adjust the volume with the adjustment button. Belt-clip Specifications: Transmitter Frequency control: Phase Locked Loop Carrier Frequency: 433MHz Modulation Mode: FM Input Level: Virtual Value 500mV The frequency response: 60Hz-15kHz The SNR: >45dB (at 1kHz) Total non-linear distortion: < 1% Transmitter power: 10mW Input level: valid values of 500 MV The transmitter power supply: 2 x 1.5V AA alkaline batteries The receiver power supply: battery, 5th section Package contents: 1 Transmitter 5 Receiver 1 Headset Mic 5 Earphone 1 Adaptor Plug 1 Audio Cable.The item "Professional Sets UHF Tour Guide Wireless System 1 Transmitter 5 Receivers" is in sale since Monday, April 7, 2014. This item is in the category "Musical Instruments & Gear\Pro Audio Equipment\Microphones & Wireless Systems". The seller is "photowoow" and is located in hongkong. This item can be shipped worldwide.