Pin-spot audio design using double sideband modulation with suppressed carrier and logarithmic subband decomposition for speech leakage reduction

抄録

Parametric array loudspeakers achieve sharp directivity in audible sound by utilizing nonlinear interactions among ultrasounds in air. Conventionally, pin-spot audio has been realized by emitting ultrasounds separately. However, nonlinear interactions among sideband components lead to speech leakage outside the audio spot. A previous study applied subband decomposition to the sideband of an amplitude-modulated signal, which altered the spectrum of the leaked sound but provided limited controllability because only one sideband was processed. This study proposes a pin-spot audio design that combines double sideband modulation with suppressed carrier and subband decomposition applied across both upper and lower sidebands. By designing the structures of the two sideband spectra, the proposed method controls nonlinear interactions across them, producing more complex patterns in the resulting spectrum in air and reducing speech leakage. Moreover, a logarithmic subband decomposition approximately consistent with perceptual frequency spacing and an asymmetric sideband assignment between the two sidebands are introduced. As a result, speech leakage is reduced not merely by lowering the sound pressure level, but by altering the structure of the demodulated sound spectrum.