Growth of masking and the auditory filter.

The threshold for a sinusoidal signal (1, 2, and 4 kHz) centered in the ’’notch’’ of a broadband masker was determined as a function of notch width for five noise spectrum levels (10, 20, 30, 40, and 50 dB SPL). For narrow notch widths the signal‐to‐noise ratio at threshold remains constant as a function of level, which according to the critical‐ratio hypothesis implies an auditory filter of constant bandwidth. For wide notch widths the signal‐to‐noise ratio at threshold increases as a function of level and this implies an auditory filter of increasing bandwidth. If the estimates of the filter bandwidth obtained for wide notch widths are used to predict thresholds for broadband noise, the corresponding signal‐to‐noise ratios will increase as a function of noise spectrum level. The predicted increase in signal‐to‐noise ratio is very small, however, and provides a good description of most available data. In fact, the predicted increase equals that observed by Reed and Bilger [J. Acoust. Soc. Am. 53, 1039–1044 (1973)]. The increase in filter bandwidth has significant consequences only when the signal and masker are widely separated in frequency; for other conditions, the assumption of a constant filter permits accurate predictions of performance.