Method of reducing the amount of data in an audio or video signal by eliminating or reducing the data that human senses cannot perceive or cannot perceive well in a specific circumstance. Human hearing is not perfect and cannot make out all sounds all the time. However, audio and video material not perceived by people is still included in traditional storage formats. hink of a time when you were listening to the stereo system at a loud level and someone walked into the room maybe even speaking to you and you did not know they were there. Loud sounds (such as the loud music) mask or cover up lower intensity sounds (such as the footsteps or even the voice). Thus, in recorded music, many sounds are covered up and go unheard. Perceptual coding takes out these sounds. f a large drum is played at the same time a small flute is played, the flute’s sound will not be perceived – it is lost in the larger sound. In order to save valuable recording space, the sound of the flute if simply taken out. The idea is that people will not miss what they never knew was there. A great deal of data can be eliminated simply by taking out those things we cannot hear anyway, and this is the basis for perceptual coding. he technique also affects how data is allocated for the reproduction of a signal. Human hearing is most sensitive around the area of 2,000 to 4,000 Hz or so. We perceive less information from very low frequency and very high frequency data. Accordingly, more storage space is allocated to the frequencies we hear the most clearly. If we cannot hear much detail in the lowest bass ranges, then why provide that area of the signal with as much detail (as many bits of data) as the areas where our hearing is particularly acute? Perceptual coding takes this into account and allocates more data storage to the areas where we will notice it and less to those where we will not. This technique allows additional data reduction. When the signal needs the data, it gets it and when it does not need the data it does not get it (sort of like turning on all the lights in the house when you only need your desk lamp versus using just the desk lamp you need – you can conserve and use a lot less electricity). erceptual coding uses the human senses to its advantage in order to use only what data storage is necessary in order to produce a signal that will appear the same as a non-encoded signal and thus use much less data.