An efficient method of amplifying a digital signal with reduced electromagnetic interference is disclosed. The invention applies an average amplitude detector to the input signal to control the clock frequency of a pseudo-random number generator so that the clock signal decreases when the average amplitude of the signal increases. The input signal and the pseudo-random number generator are compared to generate a control signal for a switching power amplifier followed by a low-pass filter. When the average amplitude of the input signal falls below a pre-determine threshold, the switching amplifier is placed in a sleep mode.