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Technical Paper

Music Analogy: An Alternative Strategy for Sound Quality Requirements

In recent years a predominant strategy for setting sound quality (SQ) requirements has been the sensory correlation approach (also called sensory evaluation or sensory science). Some users of this approach have reported their progress in numerous papers. Other SQ practitioners have made presentations on specific topics that show the linkage to music and musical notation. These specific links point to an alternative general strategy - “the Music Analogy for Sound Quality.” This paper begins by comparing the general methods of the music analogy and sensory correlation. Some major differences will be identified and implications discussed. Some existing specific tools for the music analogy will be identified as well as some gaps that need to be filled. Finally, reasons will be presented concerning why the music analogy should be considered when developing sound quality requirements.
Technical Paper

Vehicle Panel Vibro-Acoustic Behavior and Damping

Damping treatments are widely used in passenger vehicles, but the knowledge of damping treatments is often fragmentary in the industry. In this study, vibro-acoustics behavior of a set of vehicle floor and dash panels with various types of damping treatments was investigated. Sound transmission loss, sound radiation efficiency as well as damping loss factor were measured. The damping treatments ranged from laminated steel construction (thin viscoelastic layer) and doubler plate construction (thick viscoelastic layer) to less structural “bake-on” damping and self-adhesive aluminum foil-backed damping treatments. In addition, the bare vehicle panels were tested as a baseline and the fully carpeted floor panel was tested as a reference. The test data were then examined together with analytical modeling of some of the test configurations. As expected, the study found that damping treatments add more than damping. They also add mass and change body panel stiffness.
Technical Paper

Pitch Intervals: Linking Sound Quality Engineering and Musical Acoustics

One task of sound quality engineering is to find of links between engineering measures and human perceptions of sound. Over the years, several papers have been presented at SAE N&V conferences concerning the sound quality of electrical motor sounds in automotive applications. Many papers have focused on the variation in motor speed during system operation. While some papers have suggested that a useful measure for slow variations is fluctuation strength, other papers suggest measures for dealing with non-periodic variations or the general trend in motor speed. Both sets of papers tend to describe the changes in terms of percentage of a statistic of the motor speed. While percentage is a useful engineering approach, it may not be the best way to relate how the changes will be perceived by a human listener. The alternate approach described here offers formulae, in units of scale-steps or cents, to describe the changes based on the link between engineering measures and music.
Technical Paper

Percentile Frequency Method for Evaluating Impulsive Sounds

The Percentile Frequency method originated in an attempt to quantify the frequency content of door slam sounds. The method is based on the Specific Loudness Patterns of Zwicker Loudness. Zwicker states that the area of the Specific Loudness Pattern is proportional to the total loudness. The method summarizes each Pattern as seven frequencies identifying the contributions of fixed percentages of the total area (i.e. 10%, 20%, 30%, 50%, 70%, 80% and 90%). Applying the method to each Pattern in a time series generates a family of curves representing the change in relative frequency content with time. The process, in effect, normalizes the frequency content of the impulse for loudness and reduces the data to a two dimensional plot. On a Percentile Frequency plot a simple impulse appears as a pattern of “nested, inverted check marks.” More complicated impulses, such as rattles, have more complicated shapes that are still “nested” together.