BT TX Mode Input: USB, coaxial, and optical in;Output: Bluetooth transmission. Notices:--Under the mode of USB in and Bluetooth out, the volume knob cannot work, and the LDAC codec is not supported. Because under this mode, the audio signal is not transmitted through the CT5302 chip which controls the volume. While the Bluetooth chip itself does not have the function of volume adjustment, so the volume knob on the device will be invalid at this time. --IF it is connected to a Bluetooth receiving device, double click the PAIR button to switch Bluetooth codecs of the BTA30.