Each channel module is also provisioned with unbalanced inputs for directly feeding into the transmitter channel, where an auxiliary emergency connection enables an input overmatching any transmission channel in case of emergency. The on-off switch on the front panel channel may take control over the channel transmission easily and two IR LEDs may monitor the system with a receiver at the transmitter location in a simple way. Furthermore, the test switch on the front panel may deliver a test tone on each channel and hence simplify the test on the transmission system.