On the Magnitude of Critical Ratios

Critical ratios were found at nine frequencies between 250 and 8000 Hz for a wideband masker. Three different noise levels, spaced 10 dB apart, were used. The lowest noise level for each frequency was intense enough to provide 30 dB of masking. Five listeners, with normal hearing, served as subjects. Quiet and masked thresholds were obtained by means of an adaptive procedure based on 4IFC. The critical ratios found here were considerably smaller than those traditionally reported, but they did show the expected dependence on frequency. Critical ratios for frequencies at 1000 Hz or higher, however, were found to vary systematically with spectrum level of the masker. This noise level effect, 1.4 dB change in critical ratio for 20 dB change in masker level, was statistically significant at the 0.01 level.