The preference of slope overload to granularity in the delta modulation of speech

A preference study was made to assess the relative annoyance values of slope-overload distortion and granular noise in delta-modulated speech. A recently described adaptive delta modulator was simulated at frequencies of 20 and 40 kHz, and controlled amounts of the two types of degradation were introduced into samples of a 2-second utterance. Rankings were obtained for these samples on the basis of preference judgments of nine listeners, each of whom assessed the samples, pairwise, in a tournament-type strategy. Results indicate that the speech sample exhibiting the minimum degradation on an objective, overall-noise-power basis is not subjectively the most preferred sample. Furthermore, the subjectively optimum delta modulator exhibits greater overload and lesser granularity than the objectively optimum device.