This lecture is a research result concerning the application of jitter in the fields of physical phenomena modeling, modulation and multiple access. This kind of jitter called Clock Changes is applied on stationary processes. Firstly, some physical phenomena and atmospheric channels can be modeled using stationary Gaussian delays. Secondly, stationary clock changes are used to study non uniform sampling. Furthermore, periodic clock changes can be used as a spread spectrum modulation process for digital signals. Finally, they can be viewed as a generalization of standard multiple access techniques.