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A simple mathematical model of auditory nerve activity was used to evaluate the increase in critical bandwidth with masker intensity suggested by psychophysical detection experiments. Given the masker spectrum, the model allows calculation of the excitation areas [i.e., the ranges of characteristic (best) frequencies of excited auditory nerve fibers] as a function of intensity. The results of a recent study of detection thresholds for a tone centered in the gap of a notched noise masker [D. L. Weber, J. Acoust. Soc. Am. 62, 124–129 (1977)] were analyzed. For narrow notch widths, the excitation areas completely overlap in the notch region at all intensities. The masking effect is then essentially the same as for a single wide‐band masker, and is characterized by a constant signal‐to‐noise ratio as a function of masker level. At wider notch widths, the excitation areas are separated by a gap that is inversely proportional to masker intensity. This leads to a nonlinear increase in detection threshold with masker intensity. The model thus predicts Weber's findings and supports the contention that critical bandwidth increases with masker intensity. [Work supported by NIH.]

Amplitude distributions which probabilistically describe the level variations present in third‐octave bands during speech have been obtained through the periodic sampling of the short‐term rms speech envelope in each band. Representative density functions are presented for a variety of speech materials including isolated CVC syllables and nonsense sentences spoken by male and female talkers. In general, the amplitude distributions do not have simple analytic forms, although they can be described parametrically in terms of cumulative percent levels. Typically, the range of amplitudes between the 10% and 90% cumulative levels in each frequency band exceeds 40 to 50 dB. Detailed characteristics of the density functions, however, change significantly across frequency. In the low‐frequency bands, the distributions are bimodal, reflecting distinct amplitude ranges for voiced and unvoiced speech segments. The distributions become unimodal and more peaked in the higher frequency channels. Comparisons of these results with previous characterizations of speech amplitude distributions [i.e., H. K. Dunn and S. D. White, J. Acoust. Soc. Am. 11, 278 (1940] are also presented. [Work supported by NIH.]