A class D amplifier is not a digital amplifier but a switching amplifier. The class D amplifier converts the analog signal (input) into a PWM waveform. The PWM modulator is not an ADC converter (as many think) but a frequency modulator that creates a sort of pulse train corresponding to the amplitude and frequency of the input signal. This process appears digital but this is analog. The signal is not "digitized", assigned to a numerical value; the PWM pulse train is an "analog" version of the input audio signal. The PWM waveform drives the push-pull MOSFET output stage fully on or off for each pulse. When one of the MOSFETs is on, the current flowing through it is high, but the voltage is very low, so the power is dissipated only during the short transitions between the on and off state. Similarly, when the MOSFET is off, the voltage across it is high, but the current is nearly zero. There is no power dissipation except in the on / off state transitions. The amplified PWM waveform, before being transferred to the speakers, is subjected to low-pass filtering to recover the audio waveform and to eliminate spurious ultrasonic noise.