A common method of converting analog signals into digital signals.
Pulse code modulation (PCM) devices receive analog signals with continually varying voltages and quantize these signals into discrete voltages sampled at regular time intervals, typically 8000 times per second, with each sample being 8 bits in size. This provides a total transmission rate of 64 Kbps, as in Integrated Services Digital Network (ISDN) digital telephone communication. The result of this quantization process is a series of discrete voltages over time.
The voltage levels correspond to powers of 2 and represent a series of binary numbers so that the output of a PCM device is essentially a binary number.
A typical PCM device consists of a sample-and-hold circuit that samples the analog voltage signal and holds it long enough so that an analog-to-digital converter can convert it into digital (binary) format.
A single device plus its associated software that can perform both the analog-to-digital conversion and its reverse is known as a codec or coder/decoder.