BX-4 is a Bluetooth converter with 4.0 chip. This chip offers high quality sound and makes the compatibility and integral performance more optimizing. Just use 3-pin XLR to connect console or active speaker, then using Bluetooth to connect smart phone, pad such devices to realize wireless transmission. STEREO-LINK button helps BX-4 pairing with another BX-4 to transmit the signal to audio equipments (when BX-4 has already paired with phone, tablet such Bluetooth devices).