Define Quantization Error?

Quantization by its nature introduces errors. There are two major sources of errors. One is sampling, that just takes the amplitude of the signal at a point in time and holds it until the next sample. Another source of errors comes from the quantizer that pulls up or pushes down the amplitude of the signal to its digital representation.

The quantization graph above displays the type of error levels involved in our case. This error generates an effect which is known as quantization noise. In audio or speech applications, this error takes place as noise on the output. If we take a common DSP application with a 10- to 12-bit ADC, the quantization noise is generally negligible compared to other noise sources.