THE ROLE OF ENVELOPE FLUCTUATIONS IN SPECTRAL MASKING

Two experiments are reported in this study. In the first experiment the masking effect of five different types of narrow-band maskers was compared. The masker was either a tone, a narrow-band Gaussian noise, or a multiplication noise obtained by multiplying a sinusoid with a low-pass Gaussian noise. The noise maskers had a bandwidth of either 20 or 100 Hz. In all cases the masker had a center frequency of 1.3 kHz and a duration of 500 ms. Five-point growth-of-masking functions were measured using a 2-kHz tonal target with a duration of 400 ms, temporally centered in the masker. Six subjects participated in the experiment. Although considerable intersubject differences were observed, the data of all subjects showed several common trends. First, the tonal maskers produced more masking than the noise maskers. Second, Gaussian noise maskers produced more masking than multiplication noise maskers of the same bandwidth. Finally, 100-Hz-wide noise maskers produced more masking than 20-Hz-wide maskers of the same type Differences in masked thresholds between the various masker types generally increased with masker level, and exceeded 25 dB in some conditions. The results are discussed in terms of masker envelope fluctuations. In the second experiment the masking effect was investigated for a bandpass noise at 1.3 kHz, with regular zero crossings, but with the envelope characteristics of a 100-Hz-wide Gaussian noise. Five-point growth-of-masking functions were measured using a tonal target of 2 kHz. Masked thresholds produced by this hybrid masker were not significantly different from those produced by a 100-Hz Gaussian masker, but differed significantly from those produced by 100-Hz-wide multiplication noise. This result indicates that differences in masking between Gaussian and multiplication noise are not due to their different fine structure, but to their different envelope statistics.© 1995, Acoustical Society of America. All rights reserved.