An apparatus is provided for generating a timing signal having an input for receiving a first signal indicating successive time intervals, means for receiving a second signal indicating successive time intervals, and a generator adapted to generate a timing signal based on the second signal and on a relationship between one or more time intervals of the first signal and one or more time intervals of the second signal. This arrangement enables a timing signal to be generated using a time signal produced by a source or device and to be based on a time signal produced by another source or device.