Terminology
The term "class D" is sometimes misunderstood as meaning a "digital" amplifier. While some class D amps may indeed be controlled by digital circuits, the power stage deals with voltage and current as a function of time. The smallest amount of noise, timing uncertainty, voltage ripple or any other non-ideality immediately results in an irreversible change of the output signal. The same errors will only lead to incorrect results when they become so large that a signal representing a digit is distorted beyond recognition. Up to that point, non-idealities have no impact on the transmitted signal. The difference between digital and analogue signals is that digital signals are subsequently interpreted as numbers whereas in analogue signals the exact waveform matters.
Nevertheless, the term "digital amplifier" has gained currency to denote class D amplifiers with significant amounts of digital processing in them.
Read more about this topic: Class-D Amplifier