PCM isn't really encoding per say. At least not compared to more advanced technics. PCM is just an 8bit (in it's simplest form) interger value that coresponds to the instantanious amplitude coming from the recording source, played back through a DAC at some specific rate. Ie if the value is 0 the voltage is 0, if the value is 255 the voltage is 1 etc.. repeated at a specific rate (sound cards use 8k 22.05k and 44.1k as typical values for the sampling rate) Investigate a bit on Wikipedia, there is a perplethera of information on it.