Growth-of-masking functions for several types of maskers.

Growth-of-masking functions were obtained for sinusoidal signals at three frequencies (fs), 0.25, 1.0, and 4.0 kHz, using maskers that were always higher in frequency than the signal. Five different maskers were used, chosen so as to evaluate the influence of temporal fluctuations in the maskers and of combination products produced by the interaction of components within the maskers: A sinusoid (S); a narrow-band noise with a bandwidth of 16 Hz (N); a noise with a slightly wider bandwidth equal to 0.75 times the equivalent rectangular bandwidth (ERB) of the auditory filter at each fs (W); a noise with a very wide bandwidth equal to 0.4fs and with lower cut-off frequency and spectrum level matched to those of masker W (V); and a sinusoidal carrier frequency modulated by a noise, and matched in bandwidth and center frequency to masker N (F). The center frequencies of maskers S, N, W, and F were either 1.1fs or 1.2fs. Masker S generally produced the smallest amount of masking and gave growth-of-masking functions with the shallowest slopes (much less than unity). Results were similar for maskers N and F; both produced slightly more masking than masker S and growth-of-masking functions with slightly greater slopes than masker S. Maskers W and V produced more masking than the other maskers, and gave growth-of-masking functions with steeper slopes. For all maskers, the slopes of the growth-of-masking functions were lower at the greater signal-masker frequency separation. It is suggested that the results for the two maskers with the greatest bandwidth (W and V) were influenced by combination bands produced by the interaction of components within the masker. The results for the maskers with very small bandwidths (S, N, and F), suggest that the upper side of the auditory filter increases in slope with increasing level.