The ST-SX4 accepts up to four unbalanced audio sources. Any of these sources may be selected to feed the output, or all sources may be switched off. The output from the ST-SX4 is unbalanced. Control of the module is accomplished through a single input terminal. Connection of a specified resistance between the CTRL input and ground causes the desired input to be switched on. The necessary external resistors are supplied with the ST-SX4. The ST-SX4 may be remote controlled using the RC4-ST remote control.