Mask or Masking

The effect one sound has on another by making it harder or impossible to hear. The level of masking can be defined in decibels as the threshold shift necessary to restore a masked sound to audibility in the presence of a masking sound. The experimental procedure is first to determine the threshold of the sound in a quiet room. Then the masking sound is introduced and the first sound is raised until it again becomes audible. The difference is calculated in decibels.

See: Jet Pause, Lo-Fi, Recruitment, Reverberation, Sound Pollution, Transient. Compare: Adaptation.

Masking will also occur for a few milliseconds before and after the desired sound, these phenomena being termed forward and backward masking respectively.

The three graphs show the change in the threshold of audibility produced by tones of 800 and 3500 Hz respectively and of broad band noise from 100 to 10,000 Hz. From these it can be seen (a) that low-frequency sounds disrupt auditory communication more than high-frequency sounds (compare the graphs for 800 Hz and 3500 Hz), and (b) that white or broad band noise interrupts auditory communication more or less uniformly across the frequency spectrum to an extent that for every 10 dB increase in the noise we must increase the tone by a corresponding 10 dB to make it audible.

Compare: Cocktail Party Effect, Precedence Effect.

The change in the threshold of detectability for masking by (a) a 800 Hz pure tone; (b) a 3500 Hz pure tone; (c) white noise of uniform spectrum (from Miller, Language and Communication, McGraw-Hill, N.Y., 1963, pp. 54-55, used by permission).

As a technique of soundscape design, masking can make the sonic environment more pleasant; for example, the sound of fountains at busy intersections in Madrid and Rome. However, when white noise is used to simulate this effect as, for example, in the air-conditioners of contemporary buildings (see infrasonic, Noise Criterion), the effect is liable to result in a higher Ambient Noise Level and may pose a greater aural health hazard, or communication difficulties (see Articulation Index, Speech Interference Level).

Masking effect of a fountain (at the Courthouse, Vancouver, B.C.) which increases as the recordist approaches it.