People can hear a sound in a quiet environment, even if the sound pressure level is very low, which shows that the hearing threshold of human ears can be very low. But while listening to one sound, if there is another sound (masking sound), it will affect the listening effect of human ears. At this time, the hearing threshold of the heard sound will increase. The phenomenon that the human ear's auditory sensitivity to other sounds is reduced due to the existence of a certain sound is called "masking effect".

For pure tone, the masking effect is more obvious when the frequency of acoustic signal is close to that of masking sound. Low-frequency sound has a considerable masking effect on high-frequency sound, and high-frequency sound can also mask low-frequency sound to some extent. With the increase of sound pressure level of masking sound, the frequency range of masking becomes larger and larger. Note that the masking caused by narrowband noise cannot be directly predicted from the masking experiment with broadband noise. Or conversely, Dallas has time to cover the auditorium besides frequency. Sometimes, a tone can be masked by the voice before it, which is called pre-masking. It can also be covered by the voice that follows him. This is called post-masking. The appearance of post-masking is that when the signal is cut off, it takes a while for the human ear to recover its normal hearing. For example, a short clicking sound will be heard after a popping sound, but it can't be heard. Masking effect is like a person standing in front of you will block your view, and one voice will be masked by another. That is, because of the existence of a certain sound, it is necessary to improve these sounds in order to hear other sounds clearly. The decibel number of hearing threshold increase is called masking amount. People's auditory organs can distinguish several kinds of sounds that exist at the same time, but if one of them is enhanced, it is difficult to hear or even hear other sounds.