An apparatus and method for calibrating gain difference between microphones included in a microphone array are provided. The device is operable to control a ratio of light transmitted by the device to light blocked by the device. A connection control between the first and second terminals is performed by the connection control server in response to the connection control instruction; and the connection state data of each of the first and second terminals is stored in the storage server when the connection state between the first and second terminals is changed. A process for preparing the composite according to the invention is also disclosed. The source also comprises a polarization control device comprising N programmable polarization controllers under closed-loop feedback control, one per channel, each controller being disposed between the associated phase-shifter element and channel. If appropriate, the combinations are also suitable for regulating the growth or else for controlling the yield or the constituents of sugar beet plants.