THE ROLE OF DISTORTION PRODUCTS IN MASKING BY SINGLE BANDS OF NOISE

Masking experiments with frozen-noise maskers were conducted to invest igate the role of distortion products generated by the interaction bet ween the components of a bandpass noise masker. In the first experimen t, thresholds of a 900-Hz sinusoidal signal with a duration of 50 ms ( 10-ms ramps included) were measured in the presence of bandpass noise maskers ranging from 1 to 2 kHz. In all measurements the same 500-ms n oise sample was used (frozen noise), presented at overall sound-pressu re levels of 35, 50, 65, or 80 dB. The signal was temporally centered in the masker. Four subjects participated in the experiment. Threshold variations of more than 10 dB were observed on varying the signal pha se. The pattern of threshold versus signal phase resembled a sinusoid; the signal phases at the minimum and maximum thresholds differed by a bout 180 deg. The phase pattern shifted with increasing masker level. The individual shift for the masker range of 45 dB was between 100 and 200 deg. The direction of this shift agreed with data on the phase of cubic difference tones as a function of the level of sinusoidal prima ries. In a second experiment a large number of different frozen-noise samples were used as maskers in order to evaluate the generalizability of the phase effect. Two types of noise maskers were used: a low-freq uency masker (0-800 Hz) and a high-frequency masker (1060-2000 Hz). Fo r each noise sample, thresholds of a 900-Hz signal were measured for t wo signal phases, 0 and 180 deg. An analysis of variance showed that s ignal phase played a significant role for the high-frequency, but not for the low-frequency masker. (C) 1995 Acoustical Society of America.