There is described a method of optimizing the design of an electronic device with respect to electromagnetic emissions based on frequency spreading. With the method, a designer can, for example, perform a transient simulation on the device only once, and then process the obtained signal data to add frequency spreading with specific parameters by post-processing. The resulting data can be filtered by various methods and the resulting spectrum observed. The designer can thus evaluate the reduction in electromagnetic emission level, and repeat this process by iteratively applying frequency spreading each time with specific parameters but without having to modify the schematic of the device and to perform another simulation of the device. The post-processing according to this innovation is extremely rapid as it is not a simulation process such as SPICE™, ADS™, etc. Only data is manipulated.