sentences:  No added mass is influencing the measurement, as the sensor is light itself.Techniques used to help identify NVH include part substitution, modal analysis, rig squeak and rattle tests (complete vehicle or component/system tests), lead cladding, acoustic intensity, transfer path analysis, and partial coherence.Most NVH work is done in the frequency domain, using fast Fourier transforms to convert the time domain signals into the frequency domain.