Wannamaker, R.A., S.P. Lipshitz and J. Vanderkooy, "Dithering to Eliminate Quantization Distortion," Proc. of the Annual Meeting of the Canadian Acoustical Association, Halifax, Nova Scotia, 1989 Oct. 16-19, pp. 78-86. (invited review paper).


Practical digital storage and transmission systems require the representation of infinite precision analog information with finite bit-length binary words. The attendant loss of resolution introduces distortion into the signal unless appropriate preventive measures are taken. This paper will provide a survey of the "dithering" technique, in which a small additive dither noise is introduced into the signal before analog-to-digital conversion. It will be shown that with properly chosen noise characteristics it is possible to retain the resolution of the analog system and eliminate distortion in the output at the expense of a small decrease in output signal-to-noise ratio. It will also be seen that subsequent digital signal processing can destroy the benefits thus attained if truncation or rounding are applied to the results of internal arithmetic in order to yield an acceptable output wordlength. Application of a proper digital dither before the final length reduction will ensure that this does not occur. Spectral shaping of the dither to decrease the output noise audibility in audio applications will be explored. In addition, the imminent technology of noise-shaping converters will be discussed, and the possible role of dither in such systems examined.