PCM

PCM stands for pulse code modulation.  PCM is a method of translating an analog audio signal into a digital signal - and then combining it with a high frequency carrier for transmission.  In the case of PCM, the digital code relates to the amplitude of the audio signal, and the audio signal is sampled fast enough to be sure that the audio signal is well represented by the digital code it is changed to.

The term modulation means that the low frequency voice or music or other analog sound must be raised in frequency such that it can be transmitted long distances via wireless antennas.  Higher frequencies will simply transmit further, and of course, each higher frequency is regulated to ensure only the correct wireless products operate at each carrier frequency in order to prevent interference.  The process of raising the frequency of the audio signal to the higher frequency that will be the carrier frequency for transmission is called "modulation".  Basically, the low frequency audio or digital signal as in this case is combined with the high frequency carrier.