Sound, Masking of

a physiological phenomenon that consists in the elevation of the audibility threshold of a given sound under the influence of other sounds operating simultaneously with it; quantitatively, the number of decibels to which the threshold of audibility of the masked sound increases in the presence of the masking sounds.

A tone with a frequency higher than the masking signal is masked more effectively than a tone of lower frequency. For example, the masking effect of a tone with a frequency of 1,000 hertz (Hz) is more strongly manifested at a frequency of 1,300 Hz than at 800 Hz.

Maximal masking is achieved when the masking frequency and the frequency masked are similar. The degree of masking can also be influenced by beating, subjective tones, and other phenomena. A pure tone that sounds simultaneously with white noise is masked mainly by the spectral components of the noise that are of similar frequency and within the limits of the critical band, the width of which depends on the frequency of the tone being masked. Thus, the width of the critical band is 160 Hz for a frequency of 1,000 Hz, and 700 Hz for a frequency of 4,000 Hz. In order for a given pure tone to be heard in the presence of noise, the level of the pure tone must exceed the spectral level of the white noise by an amount equal to the summed level of all components lying in the critical band.