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The loudness of powertrain noise generally increases with increasing rpm. In the case of ‘linear’ powertrain acceleration sound, the loudness versus time relationship is well described by a linear function. Two studies were conducted on powertrain linearity. The first used tests of similarity and preference to determine whether subjects could detect changes in linearity. The second used a subjective test of preference to investigate how subjects' preference varied with differing degrees of linearity. In both studies, stimulus sets were created by artificially introducing a controlled degree of non-linearity into a nominally linear powertrain sound. The results of the first study indicate that linearity is a phenomenon that naive subjects can readily detect, and that it has an effect on overall preference. Furthermore, the second study shows that preference is related to the magnitude and position of nonlinearities in the growth of loudness versus time during an acceleration run.

Squeak and rattle (S&R) noise is an important issue in the automobile industry because the presence of audible S&R in a vehicle can convey the impression of poor quality to the customer. Furthermore, addressing S&R problems can be a significant warranty cost issue. Overall-all level types of noise assessment, such as dB SPL and loudness, are not always suitable measures for S&R detection, characterization and scaling. This is primarily due to the highly dynamic temporal and localized spectral characteristics of most S&R events. In this report, Fourier and filterbank methods for the analysis of S&R events are considered, and several criteria for the detection and scaling of S&R noise are examined using data measured both in an ultra-quiet laboratory situation and in several realistic, on-road driving conditions. Recommendations are made for an analysis method that is robust across both laboratory and on-road measurement conditions.