[62v8]

PCM is the shortform of "Pulse Code Modulation".
For the layman ....
Slice a soundwave at your nominated sample rate and you end up with a lone spike that is represented as a voltage. Translate that with whatever number of bits (4/8/16/20/24 etc) you are using for the quantisation process.

This process has been around for a very long time. The fundamental step of any analog to digital conversion.

There is more to it but I'm sure you can find it if you need to.