The head unit of a car radio system is responsible for controlling the entire audio system and generating music signals 2 din & 1 din autoradio android audi a4. A music system generally requires a bundle of electronic fittings like a CD player, a radio tuner, preamp and an amplifier. But since space and comfort is a main constraint in an automobile and since all these, as single parts would occupy more space, the head unit was introduced to combine and perform the duties of all these, single handedly Though it shoulders multiple responsibilities, the major 2 functions are controlling the overall volume of the system and managing the various audio sources and frequencies in the vehicle.