The main cause of jitter are of course external interrupts, bad hardware or drivers. The main task of the OS is to provide drivers which do not block too long.

The main cause of jitter are of course external interrupts, bad hardware or drivers. The main task of the OS is to provide drivers which do not block too long. Internal kernel book-keeping tasks of course also, but the main point of OS tasks are driver requests, interrupting system tasks. Calling it noise is just strange. Noise is usually the rand() source.