Psychoacoustic and signal processing techniques for evaluating the sound quality of impulsive sounds by Dave Bogema

I attended two of the papers co-authored and presented by Michael Blommer of Ford. Both dealt with sound quality detection metrics. The first was an application for engine ticking noise. The metric developed for engine impulsive noise (ticking, knocking, etc.) is based on a two-stage approach first is a psychoacoustic processing stage, then a transient detection stage. The data presented in the paper and in the presentation itself shows that this metric performs very well at detecting engine ticking noise. In the presentation, sounds were played of two engine noise recordings, one with ticking,� one without. The metric clearly detected the impulsive sounds in the ticking� recording.

For the second application, secondary impacts in door closing events were targeted. The approach was very similar to the engine-impulsive-noise application. The only difference was that the initial transient response of the door slam was ignored. In a door-closing event, there can be several secondary impacts or sounds after the initial door closing, especially when the window is rolled part way down. These secondary sounds can occur anywhere from 50 milliseconds to several tenths of a second after the initial impact, and these secondary impacts can significantly affect door closing sound quality, and thus affect the customer's perception of overall vehicle quality. In this application, time-varying loudness was not a good metric to use, because it did not discriminate the multiple impulsive noises but lumped� them together. So, this impulsive detection metric was applied to the door closing sounds. This new metric, which incorporates both psychoacoustic processing of the sound and transient detection, worked very well in detecting secondary impacts. For this application, the initial impact is ignored, then the levels of the subsequent impacts are used to arrive at a signal-number metric.

These two applications of a sound quality metric highlight the fact that sound quality is still a developing field with many opportunities for applying sound quality concepts to generate single-number objective metrics for subjective quality concerns. In these examples, the sound quality metrics for engine impulse noise and door closing sounds have been refined to a high level, and these metrics can be used to set objective targets for these sounds, and even employed in production-line testing. As sound quality continues to increase in importance in product image and acceptability, more refined metrics such as these will be required and developed.

Review of papers: 2005-01-2482, Sound Quality Metric Development and Application for Impulsive Engine Noise�, by Michael Blommer, Alan Eden, Scott Amman, Ford Motor Company 2005-01-2471, Detecting and Classifying Secondary Impacts in Door Closing Sounds by Michael Blommer, Barry Yang, Kelly Vandenbrink, Ford Motor Company