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Roughness is an attribute often used by customers to describe one of the annoying properties of automotive powertrain sounds. However, subjective ratings of roughness do not always correlate well with the psychoacoustic unit of roughness, aspers. The discrepancy between many existing objective measures of roughness and experimentally measured perceived roughness of powertrain noise is what motivates the work described in this paper. Several subjective experiments are conducted with real powertrain sounds as stimuli to study this discrepancy. Objective measures of roughness based on an AM model as well as an auditory model of roughness are applied. The results indicate that loudness can be a confounding factor. Also, contrary to what the objective measures predicted, subjects showed poor performance in these roughness discrimination tasks. The effect of binaural cues is also investigated and test results indicate that it is not a major factor in the scaling of roughness.

Significant progress could not have been made in the Sound Quality area without the invention and development of engineering tools. For the sound engineer, the binaural recording head is a primary example of one of those tools. The use of the binaural recording head was crucial to the development of the sound characterization process and has become an essential tool in the Sound Quality areas in Ford Motor Company. A similar tool, The Ford Vehicle Vibration Simulator, has been developed for the vibration engineer. The vehicle vibration simulator (VVS) is unique, consisting of vibration of the vehicle seat (6 degrees of freedom), steering wheel (4 DOF), vehicle floorpan section (1 DOF), and the brake or accelerator pedal (1 DOF). Many vibration test systems have been developed to study human response to vibration, especially for military and space applications. To our knowledge, this is the first multi-axis, fully integrated vibration test system to be used for automotive applications.