Components are used either to reduce noise current by increasing the impedance of the current path or to reduce noise voltage by decreasing the impedance of a shunt path. A combination of these functions is often used in the design of a filter. Some components are lossy and have the property of converting radio frequency noise energy into heat. There are techniques available to the designer to reduce the generation, radiation, and conduction of unwanted noise. Manufacturers of commercial equipment exported to the European Community must make the electromagnetic compatibility Declaration of Conformity, and this will typically be made after emission and immunity testing. Where high-radio frequency currents have to be carried and it has been determined that an Electromagnetic Interference emission problem may arise, the following shielding recommendation should be followed. Coupling caused by common-mode current flow is not reduced by twisting; instead, source reduction or shielding must be used.