Signal-Adaptive and Perceptually Optimized Sound Zones with Variable Span Trade-Off Filters

Creating sound zones has been an active research field since the idea was first proposed. So far, most sound zone control methods rely on either an optimization of physical metrics such as acoustic contrast and signal distortion or on a mode decomposition of the desired sound field. By using these types of methods, approximately 15 dB of acoustic contrast between the reproduced sound field in the target zone and its leakage to other zone(s) has been reported in practical set-ups, but this is typically not high enough to satisfy the people inside the zones. In this paper, we propose a sound zone control method which shapes the leakage errors so that they are as inaudible as possible for a given acoustic contrast. The shaping of the leakage errors is performed by taking the time-varying input signal characteristics and the human auditory system into account when the loudspeaker control filters are calculated. We show how this can be performed using variable span trade-off filters known from signal enhancement, and we show how these filters can also be used for trading of signal distortion in the target zone for acoustic contrast. Numerical validations under anechoic and reverberant environments were conducted, and the proposed method was evaluated via physical metrics including acoustic contrast and signal distortion as well as perceptual metrics such as the short-time objective intelligibility (STOI). The results confirm that, compared to existing nonadaptive sound zone control methods, a perceptual improvement can be obtained by the proposed signal-adaptive and perceptually optimized variable span trade-off (AP-VAST) control method.