The Sennheiser AVX MKE2 Wireless Lav Microphone Kit is a remarkable lav mic set designed to work reliably and easily. The system constantly changes frequencies to achieve the cleanest, strongest signal possible, all with zero input from the user. A neat Auto Dynamic Range setting automatically adjusts audio levels to the recording device's input sensitivity, reducing the need to change levels and also reduces distortion. Say goodbye to AA batteries as well, the transmitter and receiver are powered by a built-in Li-Ion battery charged through the included Micro USB cable and wall plug. The transmitter will last about 15 hours and the receiver will last about 4 hours on a single charge. The receiver is also able to receive 48V power from your recording device (if applicable) and switches between phantom and battery power automatically.