The exponential increase in computation power has allowed the development of numerical simulation methods. Numerical simulation is widely used in the industries at all stages of the development process: the design aid, comparison between several solutions, validation. Virtual prototyping and optimization methods enable to meet requirements from the first physical prototype. Hydraulic power transmission, which is a mature technology providing an unrivalled specific power, is widespread for Off-Road and On-Road vehicles. Nevertheless, this kind of technology has two identified weaknesses which are energetic efficiency and noise generated during the operation. In this context, our research project focus on the analysis, the modelling and the simulation for a component set constituting a hydraulic transmission taking into account the flow and pressure ripples (hydroacoustic phenomena). Thus, our project deals with the fluid borne noise modelling applied to a hydrostatic transmission. From the state-of-the-art on hydroacoustic spread laws, this paper introduces an original method for the transition from frequency to temporal domain allowing an analysis of the unsteady behavior of hydraulic system. Then, this method is applied to characterize the hydroacoustic behavior of a rigid pipe using a simulation software. Finally, the experimental means used are presented, as well as a correlation between measurement and computation applied to a rigid pipe.