Masking
masking is based on masking properties of the human ear. In contrast: When you look at the sun and if a bird passes ahead, you do not see it because of the too predominant light of the sun. In audio, it is similar. During strong sounds, you do not hear the weakest sounds. Take as an example a piece of organ: When the organist does not play, you hear the breath in the piping, and when he plays, you no longer hear it because it is masked. Different types of psychoacoustic masking exist and are exploited in most coding systems.