A dit shorter than 0.1 second requires a higher amplitude to be heard. For durations between 10 and 100 ms, the detectable signal power is inversely proportional to duration . On the other hand, dits longer than 100 ms give no significant improvement in detectability. Is dependent on the pitch of the tone. Is dependent on the purity of the tone.
Roughness degrades detectability.
A single tone of say 500 Hz is partially masked by a band of white noise. Subjects are asked to decide presence or nonpresence of the 500 Hz signal. For example, he ear's skirt shape is much steeper on the low frequency side. The ear ignores noise that falls outside its critical bandwidth. If the noise bandwidth is lowered below the critical bandwidth, no improvement is noted.