Virtual Bass Enhancement Based on Harmonics Control Using Missing Fundamental in Parametric Array Loudspeaker

摘要

Parametric array loudspeaker (PAL) can achieve a sharp directivity by using an ultrasonic wave. However, PAL has difficulty emphasizing bass sounds compared with conventional dynamic loudspeakers because it utilizes demodulation based on nonlinear interaction in the air. Also, the sound with PAL is degraded by harmonic distortion with intermodulation. Here, we focus on the missing fundamental, a psychoacoustical phenomenon indicating that human beings perceive a pitch of fundamental by harmonics. Based on this phenomenon, virtual bass enhancement has been proposed for small dynamic loudspeakers and applied on PAL. However, those harmonic generators are not suitable enough for PAL because PAL generates much more harmonic distortion than dynamic speakers. Therefore, in this paper, we propose virtual bass enhancement on basis of harmonics control adapted to harmonic distortion of PAL. The proposed method uses missing fundamental and employs a pre-processing to reproduce the virtual bass sound by stressing harmonics of acoustic signals. It re-allocates energy to higher harmonics to amplify the demodulated sound with high-shelf filter. In addition, the proposed method controls the harmonics to cause the missing fundamental and reduce the distortion of the demodulated sound using peak filters. Finally, we confirmed the effectiveness of the proposed method through evaluation experiments.