A Doppler Correction Procedure for Exterior Pass-By Noise Testing

During a pass-by noise test, the effect of the relative speed of the vehicle is translated into the Doppler phenomenon, causing positive (approaching) or negative (receding) frequency shifts (typically 2 to 5 %) in the signal received by both microphones, which are positioned at both sides of the test track at a certain distance from the center line. These experimental realities can lead to considerable errors for order tracking (used to determine engine/powertrain contributions) and coherence analysis. A Doppler correction process has been developed to deal with these effects. The correction is based on a resampling and interpolation of the target microphone time records, using recorded information on the instantaneous vehicle position measured by means of a radar. With the classical analysis tools, the Doppler correction process can improve result interpretation. It is shown that the combination of advanced techniques like adaptive resampling, and the Doppler correction process has a positive influence in proper signal interpretation.