Noise, vibration, and harshness (NVH) is the study and modification of the noise and vibration characteristics of vehicles, particularly cars and trucks.
While noise and vibration can be readily measured, it is more difficult to make statements about harshness as it is a subjective quality. In consequence, it is often measured via a jury or by using analytical tools which were designed to reflect human subjective impressions.
In general, the sources of noise can be divided into three categories, which are aerodynamic (e.g. wind, cooling fans of HVAC), mechanical (e.g. tire contact patch and road surface, brakes) and electrical (e.g. electromagnetically induced acoustic noise and vibration coming from electrical actuators).