An approximate method for obtaining transient response from frequency response

A number of approximate methods are known for obtaining the transient response of a linear system from its frequency response when the latter is known numerically but not as an analytical function. The paper presents a new method for performing this transformation which is believed to be considerably quicker and more convenient than previous methods, and to offer a greater physical insight into the behaviour of the system. The method can be used for the inverse problem of finding the frequency response of a system from its measured transient response. It also offers a means for obtaining an analytical function which represents with known accuracy the behaviour of a system of which either the frequency response or the transient response has been measured.