Control transducer locations for virtual acoustic imaging using binaural principle

Abstract

When binaural sound signals are presented with loudspeakers, the systems inversion involved gives rise to a number of problems such as loss of dynamic range, deterioration of control performance by small errors, and room reflections. A method of overcoming these fundamental problems is proposed. A conceptual monopole transducer is introduced whose azimuthal position varies continuously as frequency varies. This gives a minimum processing requirement of the binaural signals for the control to be achieved and all the above problems either disappear or are minimized. Among a number of practical solutions to realize such optimally distributed transducers is a discretization that enables the use of conventional transducer units. As for the elevation location of the control transducers, the analysis of the spectral cues and dynamic cues is performed. The frequency response of the plant that relates transducer outputs to ear-pressure signals suggests that control transducer positions will be promising at positions in the frontal plane above the listener’s head. The analysis of the dynamic cues induced by unwanted head rotation also strongly supports the use of transducer locations in the frontal plane. Subjective experiments are performed and the methods described here are proved to be advantageous.

The binaural performance of a cross-talk cancellation system with matched or mismatched setup and playback acoustics

“…The computational system simulated the playback stage by digitally convolving the processed signals with the measured HRIRs of the loudspeakers-to-microphones. Computational simulations have been used before to measure the amount of cancellation and the ITDs of a waveform (e.g., Takeuchi et al, 2001; Hill et al, 2001; Rose et al, 2002; Orduna-Bustamante et al, 2005; Lentz et al, 2005; Bai and Lee, 2006). They tend to predict large amounts of cancellation; for instance, both Takeuchi (2001) and Bai and Lee (2006) predicted over 40 dB.…”

“…Performance was impaired if the sounds were reproduced in a reverberant room, and dramatically so if the listener was 17 cm from the optimum position in front of the loudspeakers. Nelson and colleagues (Hill et al, 2000; Takeuchi et al, 2001; Rose et al, 2002) have studied the binaural performance of a cross-talk cancellation system with two loudspeakers placed at azimuths of ±5° in a large anechoic chamber. They found accurate localizations for target azimuths ahead of the listener, although back-to-front errors were again observed, and targets with large azimuths (near ±90°) were often mislocated.…”

“…Takeuchi (2001) tested the binaural performance of a six-loudspeaker system, placed in three left/right pairs at azimuths of ±90°, ±32°, and ±3.1° presenting frequencies of, respectively, less than 450 Hz, 450 to 3500 Hz, and greater than 3500 Hz. This system — termed the “optimal source distribution” (“OSD”) system (Takeuchi and Nelson, 2002) — showed encouraging results, in that it gave smaller overall localization errors, as well as fewer back-to-front errors, than a standard two-loudspeaker system with ±5° separation.…”

“…Yang et al, 2003; Nelson and Rose, 2005; Orduna-Bustamanate et al, 2005). The values of these frequencies are inversely dependent upon the azimuthal span of the loudspeakers (Takeuchi and Nelson, 2001); they are avoided in the OSD system by a careful choice of loudspeaker spans and the frequencies they reproduce.…”

“…Accordingly, the ideal method would be to measure these HRIRs — and also calculate cross-talk cancellation filters— for each individual listener. In many circumstances, however, it may be more practical to optimize the system in advance using a single set of HRIRs, perhaps from an accurately-placed manikin, calculate from those a set of cross-talk cancellation filters which would be used for all the listeners (e.g., Damaske, 1971; Moller, 1989; Sæbø, 2001; Foo et al, 1999; Takeuchi, 2001; Lentz et al, 2005; Bai et al, 2005). In this situation there will be a difference between the listener/manikin for whom the system is set up and the listener/manikin to whom the final sounds are played back.…”