The equation describing the GAS filter’s transfer function contains auxiliary values ( m eff and l eff ), which are not directly measurable in the real system. These values make the computed transfer function hard to directly compare to measurements of the real mechanical system. However, one can clearly see from the equations and in the plots, that the GAS filter transfer function is identical to the transfer function of an IP (see figure 4.7). Both feature an isolation plateau which can be lowered by varying the position or the mass of the counter weights.