11. Why the volume is not adjustable by the volume knob in the BTA30 when in USB in, TX mode?

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.

In other mode, the volume is adjustable by the bolume knob in the BTA30.