An apparatus for detecting a transient event in an operating machine, the apparatus comprising: a controller configured to control performance of the following steps: a measurement step comprising measuring a periodic signal from a machine; a processing step comprising synchronously processing the periodic signal to track the primary frequency; a filtering step comprising removing the primary periodic component and its harmonics from the periodic signal to yield a filtered dataset; an integration step comprising integrating the filtered dataset over the remaining frequencies to yield an integrated dataset representing the periodic energy at frequencies other than the primary frequency and its harmonics; an analysis step comprising identifying a short-term transient in the integrated dataset to identify a transient disruption in the operation of the machine.