Communications engineering. Pulse Code Modulation is used to digitize analog signals. In principle it is done in three steps:
1) Sampling of the analog signals with pulse amplitude modulation. This results in discrete pulses which simulate the form of the original signal.
2) Quantization of the pulses produced in the first step by comparison with predefined voltage levels.
3) Coding of the values generated in the second step, for example with a binary code. This results in the digital transmission symbols.
Pulse code modulation is often used for coding of an analog voice signal into a digital transmission signal.