Acoustic VR System

Abstract

An acoustic VR system provides a three-dimensional acoustical sensation of an existing sound field (as at concert halls, stadiums, or disaster sites) and/or an imaginary sound field (as in movies or video games), independent of time and space. This chapter introduces the system configuration and the applications of acoustic VR systems. 13.1 System Configuration An example of a typical configuration of an acoustic VR system is shown in Fig. 13.1. The system consists of hardware (a PC, a digital audio interface, headphones, earplug-type microphones, and a head-tracker), software for signal processing, and a database (HRTF and pinna shape). The main function of the acoustic VR system is to reproduce the ear-input signals obtained in an arbitrary sound field through headphones by the signal processing described in Chap. 12. This signal processing (convolution between a sound source signal and HRIRs) is performed on the PC. Another function is to change the HRTFs to those of another direction in response to the head movement of a listener. In order to capture the direction of the listener's head, a head tracker is used. Rewriting of the HRTFs must be done within the threshold for the detection of system delay, i.e., 80 ms (Yairi et al. 2005). Various systems have adopted an individualization function for HRTFs to ensure accurate sound image localization. An example system is shown in Fig. 13.2. The external specifications of the acoustic VR system, i.e., the Sound Image Reproduction system with Individualized-HRTF, graphical User-interface and Successive head-movement tracking (SIRIUS), which was developed in the author's lab, are shown in Table 13.1. This system runs on a Windows PC. An HRIR database (response length: 512 samples) is stored on the PC. A sound source signal and HRIRs are convolved in real time in order to control the direction and distance of a sound image.