You will hear a 2k tone in ten decreasing steps of 5 dB. Count how many you can hear
2kHz tone in ten decreasing steps
Now the signal is masked with broadband noise
Next the noise has a bandwidth of 1kHz
Next Noise with a bandwidth of 250 Hz
Finally a bandwidth of only 10 Hz
This demonstration of the masking of a single 2000-Hz tone by spectrally flat (white) noise of different bandwidths is based on the experiments of Fletcher (1940). First, we use broadband noise and then noise with bandwidths of 1000, 250, and 10 Hz. In order to determine the level of the tone that can just be heard in the presence of the noise, in each case, we present the 2000-Hz tone in 10 decreasing steps of 5 decibels each. Since the critical bandwidth at 2000 Hz is about 280 Hz, you would expect to hear more steps in the 2000-Hz tone staircase when the noise bandwidth is reduced below
this value. Since the spectrum level of the noise is kept constant, its intensity (and its subjective loudness) will decrease markedly as the bandwidth is decreased.