The purpose of the frequency response matching technique is to design a digital controller such that the frequency response of the resulting closed-loop system matches a specified frequency response model. The simplex method is employed to determine the controller's parameter values which minimize a function of the error between the two responses. This method permits constraints on the controller's gain and the pole-zero locations to be applied, for example, in order to reduce the highly oscillatory response of the output of the controller, a phenomenon which can be observed when applying other frequency response matching techniques. An example illustrating the use of the method, particularly at low sampling frequencies, is given.