Lutfi R A
J Acoust Soc Am. 1986 Aug;80(2):422-8. doi: 10.1121/1.394093.
Canahl [J. Acoust. Soc. Am. 50, 471-474 (1971)] measured thresholds for a 1.0-kHz sinusoid masked either by two or by four surrounding tones. He reported four-tone masked thresholds that exceeded, by 5-7.5 dB, the energy sum of the masking produced by the individual tone pairs. The present paper reports on a series of experiments investigating the effects of several factors on this 5-7.5 dB "excess" masking. In each experiment, thresholds for a 1.0-kHz 250-ms sinusoid were measured as a function of the overall level of two or four equal amplitude sinusoids with frequencies arithmetically centered around 1.0 kHz. For conditions similar to those of the Canahl experiment, 5-6 dB of excess masking was obtained independent of the level of the masking tones. Randomly varying overall level across presentations had no effect on the excess masking. The excess masking was reduced or eliminated when the masking tones were generated using an amplitude modulation technique, when they were gated on and off with the signal, or when their waveshapes were fixed across trials. Canahl's result may reflect listeners' ability to detect the signal as a change in the waveshape of the multitone masker.
卡纳尔[《美国声学学会杂志》50, 471 - 474 (1971)]测量了1.0千赫正弦波在被两个或四个周围音调掩蔽时的阈值。他报告说，四音调掩蔽阈值比单个音调对产生的掩蔽能量总和高出5 - 7.5分贝。本文报告了一系列实验，研究了几个因素对这5 - 7.5分贝“额外”掩蔽的影响。在每个实验中，测量了1.0千赫、250毫秒正弦波的阈值，该阈值是两个或四个等幅正弦波总声级的函数，这些正弦波的频率以1.0千赫为算术中心。对于与卡纳尔实验类似的条件，无论掩蔽音调的声级如何，都获得了5 - 6分贝的额外掩蔽。在不同的呈现中随机改变总声级对额外掩蔽没有影响。当使用调幅技术产生掩蔽音调、当它们与信号一起进行门控开关或者当它们的波形在各次试验中固定时，额外掩蔽会减少或消除。卡纳尔的结果可能反映了听众将信号检测为多音调掩蔽器波形变化的能力。
