It is a perceptual audio coding scheme, exploiting the masking property of the human ear, and trying to maintain the original sound quality as far as possible. In MPEG 1 Audio standard, all three layers may use 32, 44.1 or 48 kHz sampling frequency. If the power in a band is below the masking threshold, don't encode it. If the level of the 8th band is 60dB, it gives a masking of 12 dB in the 7th band, 15dB in the 9th. MPEG Layers MPEG defines 3 layers for audio.
Basic model is same, but codec complexity increases with each layer.
Psychoacoustic model only uses frequency masking. This models a little bit of the temporal masking. PCs in ENS140 is faster and better. For PCs in the ENS138 and 136. The audio sockets are in the center of the desktop.