Quantization is the conversion of a sampled signal, which is dicrete in time but continuous in value, into a signal which is discrete in value. Quantization makes a sampled signal truely digital and ready for processing by a computer.

Sampling and quantization of an analogue signal
Sampling and quantization of an analogue signal.

As can be seen from the figure above, the value of each sample is represented by a value selected from a finite set of possible values. The difference between the unquantized sample and the quantized output is called the quantization error (or quantization noise).

See also