Comparative study of design and implementation strategies of automotive virtual surround audio systems

A comprehensive study was conducted to compare various design and implementation strategies of automotive virtual surround audio. Nowadays there is increased proliferation of multichannel audiovisual systems used in cars. However, the interior of a car is known as a notorious listening environment due to reflections in a confined space, nonideal user/loudspeaker positions, and ambient noise. It is then desirable to develop audio systems that are capable of rendering quality spatial sound fields in harsh car environments. Four design approaches are proposed for two-channel and 5.1-channel input. For two-channel input a method of reverberation-based upmixing with inverse filtering and another method of up/down mixing with weighting and delay are presented. The upmixing algorithm is used to convert twochannel signals to four-channel signals, while the downmixing algorithm does just the opposite. Inverse filters are employed to position the virtual sound images according to the 5.1 configuration. For 5.1-channel input a method of downmixing with inverse filtering and another method of downmixing with weighting and delay are presented. These processing algorithms have been practically implemented on a car. Simulations and experiments were conducted for validating the proposed spatial audio systems. Subjective listening tests were also conducted to compare these methods with the data processed by multivariate analysis of variance (MANOVA). The experimental results reveal that inverse filtering is most effective for single-passenger mode, especially at rear seats. However, if there is more than one passenger, the alternative methods may be more appropriate in terms of rendering performance and computational complexity.