At the low end of the frequency range of hearing, the ear becomes less sensitive to soft sounds, although the pain threshold as well as judgments of relatively loud sounds are not affected much. At high frequencies the change in the sensitivity is more abrupt, with sensation ceasing entirely around 20 khz. The threshold of pain increases in the top octave also. The ability to make loudness judgments is compromised for sounds of less than 200ms duration. The threshold of hearing for a particular tone can be raised by the presence of another noise or another tone.
White noise reduces the loudness of all tones, regardless of absolute level.
At low loudness levels, a band of noise will mask tones of higher frequency than the noise, more than those of lower frequency. At high levels, a band of noise will also mask tones of lower frequency, than itself. The assignment of the quality of possessing pitch in the first place depends on the duration and spectral content of the sound. If a sound is shorter than 200ms or so, pitch assignment becomes difficult with decreasing length until a sound of 50ms or less can only be described as a pop. Sounds with waveforms fitting the harmonic pattern are clearly heard as pitched, even if the frequencies are offset by some additive factor.