The SounDigital 800.4 is a highly efficient, multi-channel Class D digital amplifier engineered to deliver massive power in an ultra-compact footprint. is a highly efficient, multi-channel Class D digital amplifier engineered to deliver massive power in an ultra-compact footprint. It is widely celebrated in car audio communities for its small chassis, making it the perfect upgrade for cars, motorcycles, boats, and tight spaces where premium sound dynamics are non-negotiable.