ANALOG DITHER
Some types of quantization noise can be perceptually annoying (jagged, or "aliased" lines in computer graphics, LSB toggling that is correlated with the signal)

Dither is a low-level white noise signal added to the input before quantization for the purpose of eliminating granulation or quantization distortions:



Analog dither is added to the signal before A/D conversion, often as a result of real artifacts in the recording process (microphones, mixers, cables).