Evaluation of the perceptual fidelity of a novel rotorcraft noise synthesis technique

Abstract

A human subject experiment was recently conducted at the NASA Langley Research Center to evaluate the perceptual fidelity of synthesized rotorcraft source noise. The synthesis method combines the time record of a single blade passage (i.e., of a main or tail rotor) with amplitude and frequency modulations observed in recorded rotorcraft noise. Here, the single blade passage record can be determined from a time-averaged recording or from a modern aeroacoustic analysis. Since there is no predictive model available, the amplitude and frequency modulations were derived empirically from measured flyover noise. Thus, one research question was directed at determining the fidelity of four synthesis implementations (unmodulated and modulated main rotor only, and unmodulated and modulated main and tail rotor) under thickness and loading noise dominated conditions, using modulation data specific to those conditions. A second research question was aimed at understanding the sensitivity of fidelity to the choice of modulation method. In particular, can generic modulation data be used in lieu of data specific to the condition of interest, and how do modifications of generic and specific modulation data affect fidelity? The latter is of importance for applying the source noise synthesis to the simulation of complete flyover events.