dlevi67, "What do you call the conversion of an analogue signal to a PWM/PDM or ΔΣ modulation and its subsequent filtering to recover an amplified analogue signal?"
yes analogue still. no ones and zeroes involved here so not digital.
there is no digital (I.e. code) in a class D amp, period. your confusing the differences here. Class D has been around since 1958 well before digital anything was a thing in Audio. I'd suggest you do a google search and read up on the differences, class D was just the next letter in the alphabet after class C.