Thus, by measuring magnitudes in dB, we can account for the convolution of X and H by merely adding the dB values and adding the phase values. In addition, graphs that show how the magnitudes and phase angles change with frequency are usually plotted on a logarithmic frequency scale. This is not only convenient mathematically, but also fits pretty well with the facts of human hearing.
Human hearing is more or less logarithmic, responding to ratios rather than differences.