Class-D audio power amplifiers use switched output devices to produce power with high efficiency. Various techniques are available for controlling switching patterns. A technique called BD modulation permits filter-free operation in many applications. Class-D amplifiers can produce EMI if it is not properly controlled. Solutions to this problem are often considered black magic. However, it is reasonably easy to achieve EMC through knowledge of EMI filter component characteristics and PCB layout principles. The discussion will include operation and efficiency of Class-D amplifiers with focus on BD modulation, elements of EMC testing, filter component characteristics and proper PCB layout.