Industrial plant such as rotating machinery will generate a vibration signature comprising spectral components associated with specific primary vibration sources-rotors, bearings, moving parts. These will further excite passive, static elements such that the overall spectrum, although containing information relevant to say, balance, bearing wear, electrical faults, may be difficult to interpret. Frequency selective measurement provides the means for recovering meaningful source dependant data buried in wideband signals, and to therefore diagnose the state of specific machine components.