Band-limiting experiments were performed at noise spectrum level No=20dB SPL for simultaneous and forward masking. The threshold of signal pulses masked by masker bursts as a function of different variables, such as masker bandwidth, signal frequency, signal duration and delay time between onset of masker and onset signal was measured.
The results were as follows:
1) The data for simultaneous masking showed that the slope for subcritical bandwidth was significant for its 3dB/oct slope and the slope gradually was transferred to the broad band threshold. The data for higher frequency signal of forward masking, however, were clearly recorded as a shallower slope.
2) The masker bandwidth which was effective in producing forward masking might be narrower than the critical band measured with simultaneous masking for 0.5, 1, 2, and 4kHz signal pulses. In addition the data for simultaneous masking were well described by a level-dependent critical bandwidth upward spread.
3) As the masker bandwidth was increased by ten times of the critical band the threshold (overshoot) increased by about 10dB at onset of masker for simultaneous masking. The data for forward masking, however, threshold (suppression) decreased by approximately 10dB. The overshoot would depend upon changes in the transient response of auditory system, whereas suppression of forward masking would result from decrease in steady state response of the masker.
