The paper describes a method of analytic description of impulse response (IR) signals obtained during the test of technical object. The proposed description is based on the curve fitting to obtain the values of the parameters of analytic form of auto-correlation and power spectral density function. The impulse excitation is given into thoroughly described points of object and the proper fragment of IR is selected in the order to assure the accuracy of the curve fitting over the level of 90%. This approach enables to describe changes of IR signals in the form of percentage variations in the parameters of the auto-correlation and power spectral density function (e.g. changes from the object damage).