Using psycho-acoustics frequency masking to reduce distortion in a parametric array speaker

Abstract

Using a parametric array of ultrasonic transducers, directional sound can be generated from inaudible ultrasonic as a result of nonlinear interaction of ultrasonic wave in air. A finite amplitude ultrasonic wave that can be amplitude modulated by any audio signal is radiated from the array [Yoneyama et al., J. Acoust. Soc. Am. 73, 1532–1536 (1983)]. As a result, an audio signal is produced because of the self-demodulation effect of the modulated sound wave. This, however, generates a large distortion that is impractical. Another method [T. Kite et al., J. Acoust. Soc. Am. 103, 2871 (1998)] uses a preprocessing technique, which utilizes double integration of the square-rooted input. The resulted distortion is greatly reduced but at the expense of very wide bandwidth requirement due to the square-root operation. Various techniques to reduce the distortion by preprocessing have been discussed in previous literature. In this paper, we propose a psycho-acoustic masking scheme, coupled with a suitable modulation that will provide further reduction in distortion. The psycho-acoustic masking focus on the distortion occurred within the critical bands. Simulation and subjective testing have been done to verify the system.