Relative importance of timbral and spatial fidelity in automotive sound quality evaluation

Research Student: Dr Kathy Beresford
Principal Supervisor: Prof Francis Rumsey
Co-Supervisor: Dr Slawek Zielinski
Co-Supervisor: Dr Russell Mason
Supported by: Harman/Becker Automotive Systems

Start date: 2005
End date: 2009

Project Outline

The perceptual effects of spectral distortions in the automotive audio environment were investigated. Research has been conducted to measure the effects on basic audio quality of spectral distortions in a car environment and to identify those that are likely to require engineering and signal processing resources prior to vehicle marketing.

Limitations of automotive loudspeakers, the car environment and the interaction between loudspeakers and environment cause spectral, spatial and temporal distortions of reproduced audio. The distortions that can exist in an automotive audio environment, prior to any treatment used to prepare the vehicle for retail, were reviewed and spectral distortions identified as the predominant cause of changes in the perceived audio performance. The effects on basic audio quality of a selection of typical spectral distortions were measured in two subjective evaluation experiments, focussed on the front channels of a multi-channel automotive audio system. To explore the experimental findings, a partial least squares regression model was used to predict basic audio quality, with a good level of correlation and low error term, from metrics based on characteristics of the spectral distortions and audio items included in the experiments.

The results showed that basic audio quality was significantly affected by distortions likely to result from the interaction between dashboard- mounted centre loudspeakers and the windscreen; this would therefore need to be considered by automotive audio developers. In contrast, it was concluded that for the majority of audio items used in the research, it would be possible to band-limit the centre loudspeaker without a significant detrimental effect on basic audio quality. It was also found that degradation of basic audio quality resulting from the loss of low frequency in the centre channel could be counteracted by increased correlation in the front channels; this finding could aid automotive audio development.