Page "Data compression" Paragraph 35

The masking threshold is calculated using the absolute threshold of hearing and the principles of simultaneous masking — the phenomenon wherein a signal is masked by another signal separated by frequency, and, in some cases, temporal masking — where a signal is masked by another signal separated by time.

Equal-loudness contours may also be used to weight the perceptual importance of different components.

Models of the human ear-brain combination incorporating such effects are often called psychoacoustic models.