In environmental shaker testing applications, sigma clipping of the shaker drive signal is used to protect the test system. However, the clipped signal spectrum will no longer correspond exactly to the given power spectral density (PSD). This may cause reduced vibration test reliability and even the wrong results, especially for modal tests. Both the power spectrum equalization control algorithm and PID control strategy are presented in order to compensate for the difference between certain spectra and the clipped specification. The results show that, in the case of Gaussian random signals, the two methods show almost the same compensation effect in terms of minimum error and iterative steps. For non-Gaussian random signals, however, the PID control strategy obtained fewer iterative steps and minor errors.