There is described a method of making a linear periodically time varying system shift-invariant, comprising the following steps implemented for each input signal the sampling rate of which has to be converted: —generating a set of polyphase components based on the input signal, —feeding the generated set of polyphase components to the system, and —generating an output signal by performing interleaving, shifting and addition on signals output by the system corresponding to the generated set of polyphase components processed by the system.