Masking

Masking is the auditory phenomenon that appears when the audibility, the potentiality to be detected, of a sound is altered by the presence of another. In Sound: Analysis and Specification, only energetic masking, also known as peripheral masking, phenomena are considered (as opposed to informational masking, or central masking, which is not only directly related to the sound stimuli but is also impacted by their interpretation and more generally by the way the information is treated by the auditory cortex).

There are two types of energetic masking:

• Simultaneous masking, which occurs between different frequencies. Simultaneous masking is related to the dynamic behavior of the basilar membrane in the cochlea. It occurs when the membrane oscillation created by a sound, which would be normally detected in quiet, gets "covered" by that created by another sound, provided it is loud enough and its frequency is close enough to the first one’s. Low frequencies tend to mask higher frequencies more easily than the opposite. This phenomenon is taken into account in all loudness models. It also served as a basis for the definition of most tonality indicators.

• Temporal masking that occurs between successive sounds, whether the masker is heard before (forward masking) or after (backward masking) the target sound. Forward masking, which can occur for time gap values up to 200 ms between the two sounds, is more efficient than backward masking that only occurs if the time gap value is smaller than 20 ms. Temporal masking is taken into account in loudness models for non-stationary sounds and impulse sounds, as well as in the calculation of Fluctuation Strength.