uses prerecorded (or synthesized) waveforms, stored in memory
or on disk. Defined as such, it's difficult to call it synthesis, but
advanced techniques to modify and combine recorded sounds
bring PCM squarely into camp of flexible synthesis algorithms.
PCM is:
Easy, because you can just record things and play them back
Hard, because
if you can't record them, it's difficult to synthesize them
in the limit, it requires infinite memory and time
